chemistry unit 5 revision

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ghoran
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299183
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chemistry unit 5 revision
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2015-03-29 08:26:09
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  1. define first ionisation energy
    • enthalpy change when one mole of gaseous atoms loses one mole of electrons to form one of mole of gaseous ions (with a single positive charge) 
    • X(g) --> X+ (g) + e-
  2. write an equation to represent second electron affinity
    X- (g) + e- --> X2- (g)
  3. define lattice formation enthalpy , write an equation to show this process
    • X+ (g) + Y- (g) --> XY (s) 
    • enthalpy change when one mole of a solid ionic compound is formed from its constituent ions in the gaseous phase
  4. write an equation to represent lattice dissociation enthalpy . how does the value of this enthalpy change differ from that of lattice formation enthalpy
    • XY (s) --> X+ (g) + Y- (g) 
    • same size as above but endothermic not exothermic
  5. define electron affinity . write an equation to show this process
    • enthalpy change when one mole of gaseous atoms gains one mole of electrons to form one mole of gaseous ions (with a single -ve charge) 
    • X (g) + e- --> X- (g)
  6. write an equation to represent second ionisation energy
    • X+ (g) --> X2+ (g) + e-
  7. define enthalpy of formation . write an equation to show this process
    enthalpy change when one mole of a compound is formed from its constituent elements with all the reactants and products in their standard states
  8. state hess' law
    enthalpy change is independent of the route taken
  9. define enthalpy change
    heat energy change at constant pressure
  10. explain what a born harber cycle may be used for
    cycle that includes all of the enthalpy changes involved in the formation of an ionic compound therefor it can be used to calculate any one that is unknown
  11. why is the enthalpy change for second ionisation energy larger than that of the first ionisation energy
    more difficult to loose an electron from a positively charged ion - it is smaller and therefor requires more energy
  12. why is the enthalpy change for the second electron affinity positive
    negatively charged electron is being added to a negatively charged ion and therefor repulsion occurs and more energy is required
  13. which compound has the largest lattice dissociation enthalpy LiF or csI
    LiF --> smaller ions therefor opposite charges approach each other more closely and more energy required
  14. define oxidation 
    loss of electrons 
  15. define oxidising agent 
    electron acceptor 
  16. oxidation state of Cu in Cu(OH)2
    +2 
  17. oxidation state of V in VO2+
    +5
  18. Oxidation state of Cr in Cr2O72-
    +6
  19. what is meant by a feasible or spontaneous reaction 
    one which takes place without input of energy
  20. define the term entropy
    randomness/disorder of a system 
  21. write an equation for a chemical reaction that involves an increase in entropy from reactants to products 
    explain why there is an increase in entropy 
    • NaHCO3 (s) + HCl (aq) --> NaCl (aq) + H2O (l) + CO2 (g) 
    • gas produced therefor arrangement of particles in product is more random 
  22. what is the symbol for entropy change 
    delta s 
  23. what are the units for entropy 
    J-1Kmol-1
  24. explain why steam has a higher entropy value than steam
    at higher temperatures H2O particles spread out and are more randomly arranged compared to ordered solid 
  25. explain how the entropy change for a reaction may be calculated 
    delta s = sum delta s products - sum delta s reactants 
  26. a combination of which factors two factors govern the feasibility of a chemical reaction 
    entropy change delta s and enthalpy change 
  27. write an equation that links the two factors 
    delta G = delta H - TdeltaS
  28. what value must delta G have for a reaction to be feasible 
    less than zero 
  29. if delta H is negative and delta S is positive what does this indicate about the feasibility of the reaction 
    delta G is always negative and therefor always feasible 
  30. if delta H is positive and delta S is negative what does this indicate about the feasibility of the reaction 
    delta G is always positive therefor the reaction is never feasible 
  31. if delta H is positive and delta S is positive what does this indicate about the feasibility of the reaction 
    reaction is feasible is TdeltaS is greater than delta H i.e. reaction is more likely at higher temperatures 
  32. if delta H is negative and delta S is negative what does this indicate about the feasibility of the reaction 
    reaction is feasible if delta H is greater than TdeltaS i.e. more likely at lower temperatures 
  33. what is significant about the temperature at which delta G = 0 
    in a closed system an equilibrium exists between reactants and products . can calculate the temperature at which reaction is just feasible
  34. what can be deduced about the value of delta G when a state of change occurs and why 
    delta G = 0 an equilibrium exists between the two phases in the change of state 
  35. why is it useful to know the value of delta G for the reaction of metal compounds with carbon 
    can calculate the temperature at which the extraction of a metal from its ore just becomes feasible 
  36. why does a reaction that is thermodynamically feasible sometimes not occur at a particular temperature 
    doesn't tell us about kinetics of reaction - reaction may have a large activation energy 
  37. state two properties of elements sodium , magnesium and aluminium 
    • shiny 
    • conduct electricity 
    • react with acid to produce a salt and hydrogen 
  38. define the term rate of reaction 
    change in concentration of reactants and products with unit time 
  39. what are the units for rate of reaction 
    moldm-3s-1
  40. in a graph of conc vs time how can the rate of reaction be determined at a particular point in the reaction 
    draw a tangent to the curve at the time stated and find the gradient 
  41. describe a method for monitoring the rate of a chemical reaction 
    colorimeter to measure the change in concentration 
  42. what is the rate equation
    expression that describes how the rate of reaction depends on the concentration of the species involved (at a particular temperature) rate = K[A]m[B]n
  43. define the order of reaction 
    the order with respect to a particular species is the power to which the concentration of that species is raised in the rate equation 
  44. define the term overall order of reaction 
    the sum of the powers to which the concentrations of all the species involved in the rate equation are raised 
  45. what is the symbol for the rate constant
  46. write a rate equation to show an overall first order rate expression and give the units of rate constant
    • rate = K[A]
    • units of K s-1
  47. write a rate equation to show an overall second order rate expression and give the units for the rate equation 
    • rate = k[a][b] 
    • k = mol-1dm3s-1
  48. write a rate equation to show an overall third order rate expression and give the units 
    • rate = k[a]2[b] 
    • units mol-2dm6s-1
  49. what is the order of reaction with respect to x if a graph of rate of reaction vs conc of x gives a straight line 
    zero 
  50. what is the order of reaction with respect to y if a graph of rate of reaction vs conc of y gives a sloping straight line through the origin
    first 
  51. what is the order of reaction with respect to z if a graph of rate of reaction against the conc of z gives a sloping straight line 
    second 
  52. what happens to the value of rate constant when temperature increases 
    k increases with temperature 
  53. explain your answer in terms of a maxwell botlzmann distribution curve of molecular energies and activation energy 
    at a higher temperature a greater proportion of molecules have energy greater than activation energy 
  54. what is meant by rate determining step 
    slowest step in a reaction mechanism 
  55. consider the reaction mechanism below
    A --> B + C (slow) 
    B + D --> E (fast) 
    which is the rate determining step 
    A --> B + C
  56. which of the species A - E could appear in the rate equation 
    A
  57. 1) initial O2 3x10-3 
        initial NO 2x10-3
        initial rate 6.3x10-3
    2) initial O2 2x10-3 
        initial NO 1x10-3
        initial rate 2.8x10-3
    3) initial O2 1x10-3
        initial NO 1x10-3
        initial rate 7x10-4 use this data to calculate the order with respect to NO and NO2 and hence determine the overall rate equation and calculate a value for K and give its units . 
    • rate = k[O2]2[NO]
    • 7x10-4/(1x10-3)2 = k = 700mol-1dm3s-1

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