AS chemistry for AQA unit two

Card Set Information

Author:
ghoran
ID:
265934
Filename:
AS chemistry for AQA unit two
Updated:
2014-05-07 03:19:04
Tags:
unit two
Folders:

Description:
revision
Show Answers:

Home > Flashcards > Print Preview

The flashcards below were created by user ghoran on FreezingBlue Flashcards. What would you like to do?


  1. you can use collusion theory to understand
    how the conditions used affect the rate of a chemical reaction
  2. for a reaction to occur
    particles must collide
  3. when the particles collide in a chemical reaction they must have
    enough energy to break the existing bonds
  4. when particles collide in a chemical reaction they must collide in
    the correct orientation so that the reactive parts of the chemicals come together . this is particularly important for large molecules
  5. all this means that only a small proportion of collisions between particles in a chemical reaction
    result in a reaction
  6. activation energy Ea is the
    • minimum collision energy that particles must have to react
    • it is the minimum amount of energy that the reactants must have to form an activated complex in a transition state.
  7. in an activation complex
    the old bonds are partially broken and new bonds are partially made
  8. different reactions have different
    activation energies
  9. the lower the activation energy
    the larger the number of particles that can react at any temperature
  10. draw a diagram to show the energy change in an exothermic reaction
  11. draw a diagram to show the energy change in an endothermic reaction
  12. whats the effect of changing temperature
    • as the temperature of a sample of particles changes the kinetic energy of the particles changes 
    • as you increase the temperature of a sample you increase the kinetic energy of the particles 
    • as the temperature increases , the particles move faster so they collide more often 
    • also when the particles do collide more of the particles will have enough energy to react 
    • as a result the higher the temperature the larger the number of particles that can react 
    • however , the particles will only react of they collide in the correct orientation
  13. Maxwell-Boltxzmann distributions are
    diagrams used to represent the energy of the particles in a sample of gas at a given temperature
  14. draw a Maxwell-Boltzmann distribution curve
    n(E) represents number of particles and E represents energy
  15. notice that the maxwell-boltzmanm distribution curve isn't
    symmetrical
  16. most of the particles have energy which falls
    • within quite a narrow range with few particles having much more or much less energy
  17. notice that the line doesn't cross
    the x axis at higher energy . in fact it would only do so at infinity
  18. the line starts at the origin , showing
    that none of the particles have no energy
  19. the total area under the distribution curve represents the
    total number of gas particles
  20. draw a diagram showing activation energy and maxwell-boltzmann distributions
  21. only a small proportion of particles in the shaded part of the distribution curve have
    enough energy to reaction
  22. notice that the activation energy
    is drawn towards the right of the peak of the distribution curve .
  23. if more than half the particles and enough energy to react then
    the reaction would be too fast to be controlled safely
  24. draw a diagram to show the maxwell-boltzmann curve at different temperatures
  25. notice how the range of energies that the particles have increases as temperature
    increases
  26. the average energy of the particles ..... as the temperature increases
    average
  27. the peak of the distribute curve moves to the ..... as the average energy increases
    right
  28. the distribution of the curve becomes flatter as temperature increases because
    the total number of particles remains the same
  29. for a reaction to occur
    the reactant particles must collide and have enough energy to react
  30. as the temperature increases
    the particles move faster so they collide more often
  31. the collisions between the particles have
    more energy , so more particles have enough energy to react
  32. as a result , as the temperature increases the rate of reaction
    increases
  33. maxwell-boltzmann distribution curves at different temperatures
  34. activation energy
    the minimum energy required for a reaction to occur
  35. allotropes
    different structural modifications of an element
  36. atomic number Z
    the number of protons in the nucleus of an atom
  37. atomic radius
    half the distance between the nuclei of identical neighbouring atoms
  38. reverse reaction
    one that goes from right to left in an equation
  39. biofeul
    fuel produced from renewable plant material (biomass)
  40. bond dissociation energy
    the enthalpy change for the breaking of a covalent bond , with all the species in the gaseous state
  41. calorimeter
    apparatus used to measure heat change
  42. carbocation
    a species which contains a carbon atom that has a positive charge
  43. carbon neutral
    applies to a process which occurs without any change in the total amount of carbon dioxide present in the atmosphere
  44. catalyst
    a substance which alters the rate of a reaction without itself being consumed
  45. chain reaction
    one in which many molecules undergo chemical reaction after one molecule becomes activated
  46. chemical equilibrium
    the point at which , in a reversible reaction , both the forward and backward reactions occur at the same rate , with the concentrations of all reactants and products remaining the same
  47. contact process
    the industrial process used to manufacture sulphuric acid
  48. disproportionation
    a reaction in which the same species is simultaneously oxidised and reduced
  49. dynamic reaction
    one which proceeds simultaneously in both directions
  50. elastic collisions
    those in which no energy is lost on collision
  51. electron shells
    energy levels into which electrons are distributed
  52. electronegativity
    the power of an atom to attract the electrons in covalent bond
  53. electrophilic addition reaction
    one in which a C=C double bond becomes saturated ; the mechanism involves initial attack by electron-defficient species (electrophile)
  54. elimination reaction
    one in which an unsaturated compound is formed by the removal of a small molecule such as hydrogen bromide
  55. endothermic
    the gain of heat energy by a system ; the enthalpy change is positive
  56. endothermic reaction
    one in which heat energy is taken in
  57. enthalpy change ΔH
    the amount of heat energy released or absorbed when a chemical or physical change occurs at constant pressure
  58. exothermic
    the loss of heat energy by a system ; the enthalpy change is negative
  59. exothermic reaction
    one in which heat energy is given out
  60. fehling's solution
    contains a deep blue copper (II) complex ion which , in aldehydes (but not ketones) , is reduced , on warming  , to form a red precipitate of coper (I) oxide
  61. fingerprint region
    the region below 1500 cm-1 in an infra red spectrum
  62. first law of thermodynamics
    energy can neither be created nor destroyed , but can only be converted from one form into another
  63. forward reaction
    one that goes from left to right in an equation
  64. free radical substitution reaction
    one in which the hydrogen atom of a C-H bond is replaced by a halogen atom ; the chain reaction mechanism involves attack on neutral molecule by a radical (halogen atom)
  65. greenhouse gases
    gases in the atmosphere which absorb infra red radiation (e.g. water vapour , carbon dioxide , methane and ozone)
  66. Hess's law
    the enthalpy change of a reaction depends only on the initial and final states of the reaction and is independent of the route by which the reaction occurs
  67. homolytic fission
    formation of radicals when a covalent bond breaks with an equal splitting of the bonding pair of electrons
  68. integral mass
    relative molecular mass to the nearest whole number
  69. Le Chatelier's principle
    a system at equilibrium will respond to oppose any change imposed upon it
  70. mean bond enthalpy
    the average of several values of the bond dissociation enthalpy for a given type of bond , taken from a range of different compounds
  71. mechanism
    the steps by which a reaction occurs
  72. molecular fingerprint
    the unique entire infrared spectrum of an organic compound
  73. molecular ion
    the species formed in a mass spectrometer by the loss of one electron from a molecule
  74. nucleophilic substitution reaction
    one in which an electron rich molecule or anion (with a lone pair of electrons) attacks an electron deficient carbon atom , resulting in the replacement of an atom or or group of atoms originally attached to this carbon
  75. oxidation
    the process of electron loss
  76. oxidation state (number)
    the charge of a central atom in a complex ion would have if it existed as a solitary simple ion without bonds to other species
  77. product
    a substance formed in a reaction
  78. rate of reaction
    the change in concentration of a substance in unit time
  79. reactant
    a substance consumed in a reaction
  80. redox
    used for reactions that involved both reduction and oxidation
  81. reduction
    the process of electron gain
  82. reflux
    a process in which a reaction mixture is heated in a flask fitted with a condenser to prevent the loss of volatile substances including the solvent
  83. reversible reaction
    one which doesn't go to completion but can occur in either direction
  84. standard conditions
    usually taken as 100kPa and 298k
  85. standard enthalpy of combustion
    the enthalpy change , under standard conditions , when  1 mol of substance is burned completely in oxygen , with all reactants and products in their standard states
  86. standard enthalpy of formation
    the enthalpy change , under standard conditions , when 1 mol of compound is formed from it elements , with all reactants and products in their standard states
  87. standard state
    the normal , stable state of an element or compound under standard conditions usually 100kPa and 298K
  88. stereoisomers
    are compounds which have the same structural formula but have bonds that are arranged differently in space
  89. tollens reagent
    contains the complex ion [Ag(NH3)2]+ , which , with aldehydes (but not ketones) , is reduced , on warming , to silver
  90. unsaturated
    is applied to molecules which contain at least one C=C double covalent bond or one Carbon to carbon triple covalent bond
  91. wavenumber
    • reciprocal wavelength cm-1 , used to indicate band positions in infra red spectra 
  92. the halogens form a family of
    non metallic elements which show clear similarities and well defined trends in their properties as the relative atomic mass increases
  93. group 7 data
    x
  94. define electronegativity
    the power of an atom to attract electron density in a covalent bond
  95. what's the trend in electronegativity of the halogens
    the electronegativity of the halogens decreases as the atomic number increases
  96. to explain the trend in electronegativity of the halogens three important factors must be considered
    • THE ATOMIC NUMBER , which gives the nuclear charge . As this increases , the attraction for the bonding pair of electrons in the covalent bond may be expected to increase - doesn't support electronegativity decreases as we go down th group 
    • THE NUMBER OF ELECTRON SHELLS , which is indicated by the outer electron configuration of the atom . as this number increases , the shielding of the outer electrons from attraction by the nucleus increases . this results in the outer electrons being less strongly attracted - supports electronegativity decreases as we go down the group 
    • THE ATOMIC RADIUS OF THE ATOM . the attraction between oppositely charged particles rapidly decreases as the distance between them increases . as the radius of the atom increases , the outer electrons are further from the nucleus , which therefor attracts them less strongly - supports electronegativity decreases as we go down group 
    • the electronegativity of an element depends on a balance between these three factors . the values for electronegativity given for the halogens show that the increase in shielding and atomic radius more than compensate for the increase in nuclear charge 
  97. the large electronegativity value for fluorine means that the bond between an element and fluorine is likely to be more
    polar than the bond formed between the same element and other halogens
  98. all halogens exist as
    diatomic molecules X
  99. the attraction between the diatomic molecules in the liquid state is due to
    the weak intermolecular forces called van der waals forces
  100. van der waals forces are caused by
    temporary fluctuations in electron density within the molecules , resulting in temporary dipole attractions between the molecules
  101. the magnitude of van der waals forces increases with
    the size of the molecules . this fact explains why  , as both atomic and molecular radii of the halogens increase with increasing atomic number , the boiling points of the halogens also increases
  102. when any reagent is oxidised
    electrons are taken from it . the electrons are accepted by the oxidising agent which itself is reduced
  103. the trend in oxidising power of the halogens is characterised by a decrease from
    strongly oxidising fluorine to weakly oxidising idoine
  104. the reasons for the decreasing trend in oxidising power from fluorine to iodine down group 7 are quite complex in that they involve an overall balance of energies in the following process 1/2 X2 + e- --> X- its helpful to consider this process occurring in three stages :
    • the strength of the X-X bond (breaking to form X atoms in the gaseous phase) 
    • the affinity of an X atom for an electron (forming an X- ion in the gaseous phase) 
    • the energy released when the X- ion
  105. The three features in the previous question affect the halogens differently :
    • the very strong oxidising ability of the fluorine molecule can be attributed partly to the weakness of the F-F bond 
    • the electron affinity doesn't vary greatly from one halogen to the next , so has little effect on the relative oxidising power 
    • the fluoride ion , being the smallest , hast the most to gain from being hydrated or entering a crystal , whereas the iodine ion , being the largest , benefits much less . 
    • thus the trend is a decrease in oxidising power  from fluorine to iodine : 
    • F2 > Cl2 > Br2 > I2
  106. the relative oxidising power of chlorine , bromine and iodine can be determined experimentally in the laboratory by a series of
    displacement reactions . In these experiments , aqueous solutions of the three halogens are added separately to aqueous solutions containing the other two halide ions
  107. draw a table which shows the reactions of Cl2 (aq) with Br-(aq) and I-(aq)
    • halide - Br-(aq) 
    • observations - yellow/brown solution 
    • conclusion - Bris displaced 
    • equation 
    • 2Br- + Cl2 --> 2Cl- + Br2

    • halide - I-
    • observations - brown solution and/or black precipitate 

  108. the group 2 elements are
    metals in the second group of the periodic table . They are therefor s block elements in which the outermost electrons are in a full sub level
  109. physical properties of group 2 elements
    x
  110. on descending group 2 from magnesium to barium , the atomic radii
    increases
  111. the trend on the previous slide is due to
    the increasing number of electron shells , resulting in the outermost electrons being progressively further away from the nucleus
  112. draw a graph to show the atomic radius of the group 2 elements
  113. the first ionisation energies of the elements in group 2
    decrease down the group as the atomic radius increase and the outer electrons became increasingly shielded from the positive charge of the nucleus
  114. what type of structure does magnesium have
    hexagonal close packed
  115. what type of structures do calcium and strontium have
    face centred cubic structures
  116. what type of structure does barium have
    a body centred cubic structure
  117. the group 2 metals are elements with ..... melting points
    high
  118. in metallic the structures the positive ions (cations) (M2+ in this group) are surrounded by
    a sea of delocalised outermost electrons . there are two of these delocalised electrons for each metal ion
  119. as the metal ions become larger going down the group , the strength of the metallic bonds generally decreases
    because of the decreasing charge density of the ions means that there is less attraction for the delocalised electrons . hence causing the general decrease in melting point from calcium to strontium
  120. magnesium has a lower melting point than expected because
    it has a different crystal structure to the other group 2 metals
  121. draw a graph to shows the melting points of group 2 elements Mg to Ba
  122. the enthalpy change of a system is the
    heat energy change at a constant pressure . It is indicated by the symbol ΔH where Δ is the change in or difference in and H is enthalpy
  123. when a system gives out heat energy to the surroundings
    enthalpy is lost by the system so ΔH is negative and we say the reaction is exothermic
  124. when a system takes heat energy in from the surroundings
    enthalpy is gained by the system so ΔH is positive and we say the reaction is endothermic
  125. standard enthalpy changes occur at the
    standard pressure of 100kPa and a stated temperature usually taken as 298K . the symbol ΔHø is used for standard enthalpy changes
  126. elements and compounds are said to be in their standard state if they are
    • in their normal , stable state at 298K and 100kPa . where a compound such as water could either be a gas or liquid under standard conditions , the physical state of that substance should be clarified by a symbol or by explanation . for example H2O(l) refers to water in the liquid state , H2O(g) refers to water vapour (steam) . where elements exist in allotropic forms the particular allotrope should be specified for example C(graphite) or C(diamond) . if the allotrope isn't specified it is assumed to be the more stable form (graphite in the case of carbon)
  127. Many chemical reactions continue until one of the reactants is completely used up , and theN the reaction stops . Such reactions are said to
    Go to completion
  128. The reaction between magnesium and oxygen is a good example of a reaction that goes to completion 
    equation :
    2Mg + O2 ---> 2MgO
  129. Many other reactions however , do not go to completion and are
    Reversible
  130. When the reactants and products of a reversible reaction have different colours it is easy to demonstrate
    The reversibility of the reaction
  131. when dilute sulphuric acid is added to an aqueous solution containing yellow chromate (6) ions , the following reaction occurs , forming orange dichromate (6) ions
    • 2CrO42- + 2H+ ---> Cr2O72- +H2O
    • yellow                     Orange
  132. If an aqueous solution of sodium hydroxide is now added to the orange solution , the reaction is reversed and yellow chromate (6) ions are reformed :
    • 2Cr2O72- + 2OH- ---> 2CrO42- + H2O
    • orange                    Yellow
  133. The overall reaction can be represented by the equation
    • 2CrO42- + 2H+⇌Cr2O72- + H2O
    • Yellow             Orange 

  134. the ⇌ is used to indicate that the reaction is
    Reversible
  135. By convention , the reaction shown as occurring from left to right in the equation is called
    The forward reaction
  136. The reaction occurring in the opposite direction is called the
    Backward reaction or reverse reactioN
  137. Since the reaction still continues in both directions it is said to be
    Dynamic
  138. When both reactions occur at the same rate the Concentrations of the chromate (6) ions and the dichromate (6) ions remain constant and
    A chemical equilibrium has been established
  139. A chemical equilibrium can only be established if
    reagents are neither added to or taken from the reaction mixture
  140. When A chemical equilibrium is established
    • Reactants and products are present at all times
    • the reaction is dynamic I.e. It proceeds in all directions
    • the concentrations of reactants and products remains constant
  141. If reactants are added of if products are removed , the equilibrium is
    Displaced
  142. Other reactions which can be used in the lab to illustrate the reversibility of reactions include
    [CO(H2O)6]2+  with Cl(aq) and Fe3+ (aq) with SCN(aq)
  143. The effect on the equilibrium position of the following is considered below
    • Change in concentration 
    • change in pressure 
    • change in temperature 
    • addition of a catalyst
  144. For most reactions the qualitative effect of changing reaction conditions can be predicted using
    Le chatelier's principle
  145. Le chatelier's principle states that
    A system at equilibrium will respond to oppose any change imposed upon it
  146. If all other conditions remain the same and the concentration of any of the species involved in an equilibrium reaction is changed then the concentrations of other species is also changed . Le chateliers principle can deduce the the changes that occur . For example if the concentration of a reactant is increased , or the concentration of a product is decreased
    The Position of equilibrium moves to the right and more product is formed
  147. consider the reaction CH3COOC2H+ H2O ⇌
  148. If there is a higher conc of reactants than there will N
    be more products
  149. If there's a lower conc of reactants then
    There's less producT
  150. If there's a higher conc of producT
    Theres more reactants
  151. If theres a Lower conc of product then
    Theres less reactants
  152. Draw a table to show the reactions of Br2 (aq) with Cl- (aq) and I(aq)
    X
  153. Draw a table to show the reactions of I(aq) with Cl- (aq) and Br(aq)
    X
  154. These results confirm the oxidising power by showing that
    • Chlorine will displace bromine and iodine 
    • bromine will displace iodine but not chlorine 
    • iodine will not displace either chlorine or bromine
  155. the symbol θ shows that the change is measured
    under standard conditions
  156. the standard enthalpy of combustion is defined as the
    enthalpy change , under standard conditions , when 1 mol of a substance is burned completely in oxygen , with all reactants and products in their standard states
  157. accurate enthalpies of combustion are determined by
    an experiment in a bomb calorimeter
  158. in a school lab i is possible to measure enthalpies of combustion using
    simple apparatus such as spirit burners but these usually give values which are not sufficiently exothermic . the main error is due to an inability to measure heat energy which is lost to the surroundings
  159. standard conditions are usually taken as
    100 kPa and 298 K at this temperature water os usually taken to be a liquid
  160. enthalpies of combustion are determined experimentally by using a
    calorimeter
  161. whats the symbol for standard enthalpy of combustion
    ΔHΦc
  162. whats the symbol for standard enthalpy of formation
    • ΔHΦf
  163. the standard enthalpy of formation is defined as
    the enthalpy change under standard conditions , when 1 mol of a compound os formed from its elements with all reactants and products in their standard states
  164. by definition , for an element the standard enthalpy of formation must be
    0
  165. enthalpies of combustion are usually determined indirectly using
    Hess' law
  166. the heat energy , q , required to change the temperature of a substance by an amount ΔT can be calculated using the expression
    • q = mcΔT
    • where :
    • m is the mass of the substance in kg
    • c is the specific heat capacity with the units KjK-1kg-1
    • ΔT is temperature in kelvins
    • q is heat energy in kj
  167. for many chemical reactions in aqueous solution it can be assumed that the only substance heated is
    water , which has a specific heat capacity of 4.18 kjk-1kg-1
  168. for enthalpy changes the mass of water must be  in
    kg
  169. negative signs in enthalpy calculations appear because
    the reaction is exothermic
  170. 100cm3 of water has a mass of
    0.1kg
  171. the first law of thermodynamics states that
    • energy can neither be created nor destroyed , but can be converted from one form into the other 
    • the first law of thermodynamics is also similar to the principal of conservation of energy
  172. Hess' law is a special case of the first law of thermodynamics 
    Hess's law states that
    the enthalpy change of a reaction depends only on the initial and final states of the reaction and is independent of the route by which the reaction occurs
  173. the overall enthalpy change for a multistep reaction can be calculated using the expression
    ΔH = (ΔH step one + ΔH step 2 + ...) = ΣΔH all steps
  174. it follows from Hess's law that the enthalpy change of a reaction is the
    sum of the individual enthalpy changes of each step into which the reaction can be divided , , regardless of their nature
  175. Hess' law can be used top determine ΔH values for reactions where
    direct determination is difficult . for example , the enthalpy change for any reaction can be determined if the enthalpies of combustion of the reactants and products are known . thus the standard enthalpy of formation can be calculated
  176. enthalpy changes for reactions can also be determined from
    tabulated values of enthalpies of formation
  177. the bond enthalpy for a diatomic molecule is also known as the
    bond dissociation energy
  178. bond dissociation energy refers to
    • the enthalpy change for the following process , where all species are in the gaseous state 
    • A-B (g) ----> A(g) + B(g)
  179. in polyatomic molecules it is correct to say the term
    mean bond enthalpy
  180. the mean bond enthalpy is the
    average of serval values of the bond dissociation enthalpy for a given type of bond , taken from a range of different compounds
  181. bond enthalpy calculations apply only to
    reactions in the gaseous state
  182. mean bond enthalpies can be used to calculate
    the enthalpy change for simple reactions
  183. the mean bond enthalpies of the reactant bonds that are broken are
    • added together . from this value is subtracted the sum of the bond enthalpies of the product bonds that are formed . the difference is the overall enthalpy change 
    • ΔH = Σ(mean bond enthalpy of bonds broken) - Σ(mean bond enthalpy of bonds formed)
  184. it isn't always necessary to consider all the bonds in the reactants and products we can just consider the
    bonds that are broken and the bonds that are formed
  185. when two substances reacts particles of one of the substance must
    collide with particles of the other .
  186. however not all
    collisions result in a reaction
  187. this situation arises because
    particles will only react when they collide with sufficient  energy
  188. the minimum energy for reaction is known as
    the activation energy
  189. in addition before a reaction can happen it is often necessary for
    the orientation of molecules to be correct on collision
  190. in a sample of gas or liquid , the molecules are in constant motion and collide both with each other and with the walls of their container . such collisions are said to be
    elastic i.e. no energy is lost during the collision but energy can be transferred from one molecule to another
  191. consequently at a given temperature molecules in a particular sample will have a
    spread of energies about the most probable energy
  192. maxwell and boltzmann derived a theory from which it is possible to draw curves showing how these energies are distributed . a plot of the number of molecules against energy is known as the maxwell Boltzmann curve . draw a typical curve and state what the area under the curve represents
    the area under the curve represents the total number of molecules in the sample
  193. the distribution curve has several important features
    • there are no molecules with zero energy and only a few with very high energies 
    • there is also no maximum energy for molecules - the curve approaches zero asymptotically 
    • the most probable energy of a molecule corresponds to the maximum of the curve
    • Emp is the most probable energy and E bar is the average energy
  194. if the temperature of the sample is increase from T1 to T2 the average energy of the molecules
    increases , and the most probable energy of the molecules increases . the spread of energies also changes and the shape of the distribution curve changes . for a fixed sample of gas the total number of molecules remains the same so the area under the curve remains the same
  195. draw a maxwell boltzmann curve at two different temperatures
    • the curve for the higher temperature is broader , has a lower peak , apart from at the origin it is always to the right of the lower temperature curve 
    • the area under each curve however is the same because this represents the total number of molecules
  196. the rate of reaction is defined as
    the change in concentration of a substance is unit time
  197. when a graph is plotted of the concentration of a reagent or product against time , the rate of reaction at a particular time is given by the
    • gradient of the graph at that time 
    • with units concentration time-1 commonly moldm-3s-1
  198. the rate of reaction is impacted by
    • the concentration of reagents in a solution or the pressure of gaseous reagents 
    • the surface area of any solid reagent 
    • the temperature 
    • the presence of a catalyst
  199. collision theory can be used to
    explain how these factors impact the rate of reaction
  200. increasing concentration of a reagent
    • increases the number of particles in a given volume 
    • increases the collision rate
    • hence the chance of productive collisions increases
    • this change increases the rate of reaction
  201. as the reaction proceeds ,
    reagents are used up , so their concentrations fall . the rate is therefor greatest at the start of a reaction . on a concentration time graph the initial gradient is the steepest (most negative) . the gradient falls to zero at the completion of the reaction
  202. draw a graph to show the fall in concentration of reagent with time at constant temperature
  203. when one reagent is a solid , the rate of its reaction with a gas or with a substance in solution is increased if
    the solid is broken into smaller pieces . this process increases the surface area
  204. increasing the surface area of a solid
    allows more collisions to occur with particles of the other reagent
  205. when an ionic solid is dissolved in a solvent
    its particles are completely separated so that the rate is increased even further and the reaction may become almost instantaneous . precipitates form as soon as the correct solutions are mixed as free ions in the solution can easily collide and react
  206. an increase in temperature always
    • increases the rate of reaction 
    • according to kinetic theory , the mean kinetic energy is proportional to the temperature 
    • at higher temperatures particles have more kinetic energy so move more quickly 
    • so there are more collisions in a given time 
    • the mean energy of the particles is increased 
    • so there are more particles with above the activation energy 
    • so there are more successful collisions
  207. the activation energy of a reaction
    is the minimum energy required to make a reaction occur 
  208. the number of collisions between molecules with sufficient energy i.e. the number of productive collisions , and therefor the rate of reaction is very much greater at the higher temperature . consequently 
    small temperature increases can lead to large increases in rate 
  209. Edoesn't change with temperature but
    the number of molecules with > energy than this does 
  210. draw a graph to show the change of rate as temperature rises 
  211. many reactions - including several which are very exothermic - don't occur because the 
    activation energy is too high . for example petrol reacts with oxygen in air in a very exothermic reaction , but petrol air mixture exists in the tank of a car will only react if sparked 
  212. a catalyst is a substance which
    alters the rate of reaction without itself being consumed during the reaction , most of the catalysts used are positive catalysts : they increase the rate of reaction 
  213. an example of a negative catalyst is 
    i.e. one which slows the rate of reaction is antimony oxide which is used as a flame retardant in plastics 
  214. a positive catalyst operates by 
    • providing an alternative route or reaction mechanism which has a lower activation energy Ecat than the uncatalysed route 
  215. the catalyst has no effect on 
    • the overall enthalpy change for the reaction 
    • the catalyst also has no effect on the equilibrium position since this depends only on the relative energies of the reactants and products 
  216. draw a reaction profile showing an uncatalysed and a one step catalysed reaction 
    this diagram shows a one step catalysed reaction . in many cases the catalysed reaction occurs in more than one step and a double humped reaction profile will be seen 
  217. draw a reaction profile showing an uncatalysed and two step catalysed reaction  
  218. a catalyst which lowers the activation energy from Eto Ecat will 
    produce many more molecules that are able to react . in the presence of a catalyst , therefor , the reaction rate is increased 
  219. draw a maxwell Boltzmann curve showing the effect of a catalyst on activation energies 
  220. many chemical reactions continue until
    one of the reactants is completely used up , and then reaction stops such reactions are said to go to completion . the react ion between magnesium and oxygen is a good example of a reaction that goes to completion 
  221. many other reactions however don't go to completion and are 
    reversible 
  222. when the reactants and products have different colours it is easy to 
    demonstrate the reversibility of a reaction
  223. for example when dilute sulphuric acid is added to an aqueous solution containing yellow chromate (6) ions , the following reaction occurs forming orange dichromate (6) ions : 
  224. if an aqueous solution of sodium hydroxide is now added to the orange solution , the reaction is reversed and yellow chromate (6) ions are reformed 
  225. the overall reaction can be represented by the equation 
  226. by convention the , the reaction shown as occurring from left to right in the equation is called the 
    forward reaction
  227. and the reaction occurring in the opposite direction is called the
    reverse reaction 
  228. since the reaction continues in both directions it is said to be 
    dynamic 
  229. when both reactions occur at the same rate the concentrations remain constant and a 
    chemical equilibrium has been established 
  230. a chemical equilibrium can only be established if 
    reagents are neither added to nor taken from the reaction mixture 
  231. when a chemical equilibrium is established 
    • reactants and products are present at all times 
    • the reaction is dynamic 
    • the concentration of reactants and products remains constants 

  232. if reactants are added or if products are removed , the equilibrium is 
    established 
  233. other reactants which can be used in the lab to show the reversibility of reactions include 
    [Co(H2O)6]2+ with Cl- aq and Fe3+ aq and SCN- aq
  234. the effect on the equilibrium position of the following is considered below 
    • change in concentration 
    • change in pressure
    • change in temperature 
    • addition of a catalyst 
  235. for most reactions the qualitative effect of changing reaction conditions can be predicted using 
    Le Chatelier's principle 
  236. Le Chatelier's principle states that 
    a system at equilibrium will respond to oppose any change imposed upon it 
  237. if all other conditions remain the same and the concentration of any of the species involved in an equilibrium reaction is changed then 
    the concentrations of the other species must change 
  238. Le Chatelier's principle can be used to deduce the changes that occur . for example if the concentration of a reactant is increased , or the concentration of one of the product is decreased the position of the equilibrium 
    moves to the right and more product is formed 
  239. consider the reaction 
    CH3COOC2H5 + H2O -> CH3COOH + C2H5OH 
    a)                     b)        c)                d) 
    if a little more of a) or b) is added some of the additional reagent reacts and the 
    equilibrium position is shifted to the right . as a result the equilibrium yields of c) and d) are both increased 
  240. consider the reaction 
    CH3COOC2H5 + H2O -> CH3COOH + C2H5OH a)                     b)        c)                d) 
    if more c) and d) is added the equilibrium is displaced to the 
    left and the equilibrium mixture will contain more a) and b) 
  241. changes in total pressure have a significant effect on the composition of a mixture at equilibrium only if the reaction 
    involves gases
  242. the changes observed are due to 
    changes in the concentrations of the species present 
  243. an increase in pressure , according to Le Chatelier's principle , will
    displace the equilibrium in a direction that tries to reduce the increased pressure - the system responds by decreasing the number of moles of gas present thus lowering the total pressure . the converse also applies 
  244. consider the reaction
    CH4 g + H2O g -> 3H2 g + CO g 
    in this equation the total number of moles of gaseous reactants is 2 and the number of moles of gaseous products is 4 . thus a a given temperature the equilibrium amount of products can be increased by 
    reducing the total pressure , so the system responds by moving to the right to produce a greater number of moles in a gas in an attempt to increase the pressure 
  245. if pressure is lowered what happens to the rate of reaction 
    it's reduced 
  246. a change in temperature alters the rate of both the forward and backward reactions . these are changed by different amounts , so the position of the equilibrium is altered . the simple rule which says that a system at equilibrium will react to oppose any change upon it (Le Chatelier's principle) can be used to predict the effects of a change in temperature an increase in temperature is opposed by a movement of the position of equilibrium , either to the left or right , in order to 
    absorb the added heat energy . heat energy is absorbed by moving in the endothermic direction 
  247. a decrease in temperature is opposed by a movement of the position of equilibrium , either to the left or right in order to 
    gain the lost heat energy , heat energy is gained by moving in the exothermic direction
  248. in an exothermic reaction heat energy is evolved . an increase in temperature requires the 
    removal of the added heat energy by a shift in the endothermic direction . the equilibrium position is displaced to the left and the equilibrium mixture contains a lower concentration of products . it is important to remember that although the new equilibrium mixture obtained at a higher temperature contains less product , the time taken to reach this new equilibrium is reduced because of the increased rate of reaction 
  249. H2 + I-> 2HI is an exothermic reaction at 298K this equilibrium lies far to the right and the reaction mixture at equilibrium contains a high % of 
    HI if the temperature rises then the % of HI decreases 
  250. In an endothermic reaction heat energy is absorbed . An increase in temperature requires the 
    Replacement of the lost heat energy , once again by an equilibrium shift in the endothermic direction . In this case the equilibrium position is displaced to the right and the equilibrium mixture contains a higher concentration of products 
  251. Thus for an endothermic reaction an increase in temperature 
    Increases the equilibrium concentration of the products  
  252. N2 + O2 => 2NO this is an endothermic reaction 
    at 298K the equilibrium lies far to the left so that the equilibrium mixture contains almost no NO . Increasing the temperature 
    Increases the equilibrium yield of NO but this is still to small for the direct combination of nitrogen and oxygen to be an economically viable method of preparing NO 
  253. the effects of changes in temperature on equilibria can be summarised as follows 
    An increase in temperature always displaces the equilibrium in the endothermic direction  
  254. Draw a table to show the effects of temperature changes on equilibria 
  255. the addition of a catalyst to a mixture at equilibrium has no effect on the composition of 
    The equilibrium mixture because a catalyst causes an equal increase in the rates of both the forward reaction and the backward reactions which themselves are at equal equilibrium . hence the equilibrium position is archived more quickly but the composition of the equilibrium mixture is unchanged 
  256. Many chemicals are manufactured on a large scale . The processes used are designed of give the optimum yield . 
    All the factors which affect the position of a particular equilibrium mixture must be carefully considered 
  257. Ethanol and methanol are Important organic compounds which are increasingly being used s 
    Fuels . Both these alcohols are manufactured on a large scale  
  258. Ethanol is produced industrially by
    fermentation or hydration of ethene 
  259. What are the equations for the hydration of ethene to produce ethanol 
    • C2H4 + H2O --> C2H5OH 
    • the energy change is negative 
  260. What type of reaction is the hydration if ethene 
    Exothermic 
  261. Le chatelier's principle predicts that  
    this reaction will be opposed by an increase in temperature , so the best equilibrium yield of ethanol will be obtained at low temperatures . However at low temperatures the rate of reaction is slow and although a high equilibrium yield can be achieved it may take a long time to reach equilibrium . Increasing the Temperature speeds up the rate of attainment of equilibrium . A compromise between yield and speed of reaction is clearly necessary and a typical operating temperature for this reaction is around 300°C 
  262. The equation shows that 2 mol of gaseous reactants form 1 mol of gaseous products. Application of Le Chatelier's principle predicts that the hydration of ethene will be  
    Favoured by a high pressure 
  263. The pressure used is a compromise between 
    the cost of generating a high pressure and the additional value of the increased equilibrium yield . A typical pressure for this reaction is 6.5 MPa 
  264. what catalyst is used 
    H3POthis catalyst increases both the forward And backward reactions to the same Extent . hence the time taken to reach equilibrium is reduced but the equilibrium yield of of ethanol is unaltered 
  265. Methanol is produced industrially by the 
    Reaction between carbon monoxide and hydrogen 
  266. what's the equation 
    CON+ 2H=> CH3OH the reaction is exothermic 
  267. The equation shows that 3 mol of gaseous reactants form 1 mol of gaseous product . Application of Le Chatelier's principle predicts that 
    A high equilibrium yield will be obtained at high pressure . Again the cost of generating high pressure will be balanced agains the value of the increased yield of methanol . A typical pressure used in the industry is around 5MPa 
  268. Since the reaction is exothermic application of le Chatelier's principle predicts tha a high equilibrium yield of methanol will be obtained at a 
    LoW Temperature however as the rate of reaction will be slow at a relatively low temperature a compromise is again required and a typiCal operating temperature is around 400°C 
  269. The Time required for the reaction to reach equilibrium is reduced by the use of a Catalyst
    A mixture of chromium (3) oxide Cr2Oand zinc oxide ZnO
  270. Both methanol and ethanol can be mixed with 
    Petrol to produce fuels for internal combustion engines 
  271. Ethanol is of increasing importance as 
    A constituent of motor car fuels most spark ignited petrol engines will operate efficiently with petrol ethanol blends containing up to 10% ethanol 
  272. Methanol isn't as .... As petrol . Some vehicles including drags racers use methanol as their main fuel source and methanol has also been used to fuel Indy 500 racing cars 
    Flammable 
  273. The anhydrous ethanol used in petrol ethanol blends must not contain 
    More than 1% water 
  274. Modern flexible fuel vehicles are designed to
    Use petrol ethanol blends containing up to 85% ethanol
  275. the group 2 elements are 
    the metals in the second group of the periodic table . they are therefor s block elements in which the outermost electrons are in a full s sub shell 
  276. draw a table showing some important physical properties in the group 2 elements 
    x
  277. on descending the group from magnesium to barium what happens to the atomic radii
    it increases this is due to the increasing number of electrons resulting in the outermost electrons being progressively further away from the nucleus
  278. on descending the group from magnesium to barium what happens to the ionisation energy 
    it decreases this is because the atomic radius  increases and the outermost electrons become increasingly shielded from the positive charge of the nucleus 
  279. the group 2 elements are metals with ... melting points 
    high 
  280. in metallic structures 
    the positive ions are surrounded by delocalised electrons 
  281. how many delocalised electrons are there for each Mg2+ ion 
  282. on descending the group from magnesium to barium what happens to the melting points 
    they decrease . this is because the strength of the metallic bonds generally decreases as we go down the group because of the decreasing density of charge of the ions which means there is less attraction between the delocalised electrons and positive metal ions 
  283. the expected general decrease in melting point calcium to strontium can be seen . magnesium has a lower melting point than expected because 
    it has a different crystal structure from the other metals 
  284. what type of structure does magnesium have 
    a hexagonal close packed structure 
  285. what type of structures do strontium and calcium have 
    face centred cubic structures 
  286. what type of structure does barium have 
    a body centred cubic structure 
  287. the reactivity of group 2 elements with water ..... on descending the group
    increase 
  288. magnesium reacts only bey slowly with cold water :
    Mg + H2O --> Mg(OH)2 + H2
  289. burning magnesium reacts rapidly with steam : 
    Mg + H2O --> MgO + H2
  290. the other group 2 metals - calcium , strontium and barium - react with cold water , releasing 
    • hydrogen with increasing vigour as the group is descended . for example : 
    • Ca + 2H2O --> Ca(OH)2 + H2
  291. on descending the group from magnesium to barium what happens to the solubility of the hydroxides of the metals  
    increases 
  292. magnesium hydroxide is only sparingly soluble in 
    water 
  293. calcium hydroxide dissolves to form 
    lime water , but isn't as soluble as strontium hydroxide 
  294. barium hydroxide is soluble in water and produces 
    strongly alkaline solutions 
  295. magnesium hydroxide is used as an 
    • antiacid for the relief of indigestion caused by excess acid in the stomach :
    • Mg(OH)2 + H+ --> Mg2+ + 2H2O
  296. magnesium hydroxide also acts as a 
    laxative and is used to relieve constipation . it is taken orally either as chewable tablets or in a suspension often called milk of magnesia 
  297. calcium hydroxide is used by 
    farmers to reduce soil acidity , so that a wider range of crops can be grown , and to provide calcium ions which are essential for plant growth 
  298. the lime used by farmers is often a mixture of 
    calcium carbonate and calcium hydroxide 
  299. on descending the group from magnesium to barium what happens to the solubility of sulphates 
    decreases from the soluble magnesium sulphate to the insoluble barium sulphate 
  300. in the lab the insolubility of barium sulphate is used as a 
    • test for the presence of sulphate ions in solution . dilute acid and a solution of barium ions are added to the solution under test the appearance of a white precipitate indicates the presence of sulphate ions 
    • Ba2+ + SO42- --> BaSO4
  301. in the absence of acids in the previous test carbonate ions interfere with the test because
    barium carbonate is also a white solid insoluble in water
  302. the carbonate ions are removed by adding either
    • hydrochloric or nitric acid . the acid reacts with the carbonate ions to generate carbon dioxide gas , thereby removing them from solution and preventing the precipitation of barium carbonate 
    • 2H+ + CO32- --> CO2 + H2O
  303. Barium sulphate blocks
    X rays and isn't toxic (as it is so insoluble in water and body fluids) , it is used in medicine to aid the
  304. when a halide ion behaves as a reducing agent , it 
    looses an electron to the reagent its reducing ; this process is the reverse of that in which a halogen molecule acts an oxidising agent 
  305. the trend in reducing power of the halide ions shows a decrease from 
    • the strongly reducing iodine ion to the non reducing fluoride ion
    • I- > Br- > Cl- > F-
  306. the trend in the reducing power of the halide ions is shown in the reaction of 
    sodium halide salts with concentrated sulphuric acid 
  307. the oxidation state of sulphur in sulphuric acid is +6 . this can be reduced to 
    +4 , 0 or -2 depending on the reducing power of the halide ion 
  308. observations of concentrated sulphuric acid with solid sodium halides
    sodium fluoride - a
    sodium chloride - b 
    sodium bromide - c
    sodium iodide - d 
    • a - steamy fumes 
    • b - streamy fumes
    • c - steamy fumes , colourless gas , brown fumes 
    • d - steamy fumes , colourless gas , yellow solid , smell of bad eggs , black solid/purple fumes 
  309. products and type of reaction of concentrated sulphuric acid with solid sodium halides 
    sodium fluoride - a
    sodium chloride - b 
    sodium bromide - c
    sodium iodide - d 
    • a - HF (acid based F- acting as a base)
    • b - HCl (acid based Cl- acting as a base) 
    • c - HBr (acid based Bracting as a base)
    •      SO2 (redox - reduction product of H2SO4
    •      Br2 (redox - oxidation product of Br-
    • d - HI 

What would you like to do?

Home > Flashcards > Print Preview