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^{-}
write an equation to represent second electron affinity
X^{-} (g) + e^{-} --> X^{2-} (g)
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
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
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)
write an equation to represent second ionisation energy
X^{+} (g) --> X^{2+} (g) + e^{-}
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
state hess' law
enthalpy change is independent of the route taken
define enthalpy change
heat energy change at constant pressure
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
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
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
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
define oxidation
loss of electrons
define oxidising agent
electron acceptor
oxidation state of Cu in Cu(OH)_{2}
+2
oxidation state of V in VO_{2}^{+}
+5
Oxidation state of Cr in Cr_{2}O_{7}^{2-}
+6
what is meant by a feasible or spontaneous reaction
one which takes place without input of energy
define the term entropy
randomness/disorder of a system
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
gas produced therefor arrangement of particles in product is more random
what is the symbol for entropy change
delta s
what are the units for entropy
J^{-1}Kmol^{-1}
explain why steam has a higher entropy value than steam
at higher temperatures H_{2}O particles spread out and are more randomly arranged compared to ordered solid
explain how the entropy change for a reaction may be calculated
delta s = sum delta s products - sum delta s reactants
a combination of which factors two factors govern the feasibility of a chemical reaction
entropy change delta s and enthalpy change
write an equation that links the two factors
delta G = delta H - TdeltaS
what value must delta G have for a reaction to be feasible
less than zero
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
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
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
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
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
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
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
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
state two properties of elements sodium , magnesium and aluminium
shiny
conduct electricity
react with acid to produce a salt and hydrogen
define the term rate of reaction
change in concentration of reactants and products with unit time
what are the units for rate of reaction
moldm^{-3}s^{-1}
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
describe a method for monitoring the rate of a chemical reaction
colorimeter to measure the change in concentration
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}
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
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
what is the symbol for the rate constant
k
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}
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^{-1}dm^{3}s^{-1}
write a rate equation to show an overall third order rate expression and give the units
rate = k[a]^{2}[b]
units mol^{-2}dm^{6}s^{-1}
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
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
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
what happens to the value of rate constant when temperature increases
k increases with temperature
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
what is meant by rate determining step
slowest step in a reaction mechanism
consider the reaction mechanism below A --> B + C (slow) B + D --> E (fast)
which is the rate determining step
A --> B + C
which of the species A - E could appear in the rate equation
A
1) initial O_{2} 3x10^{-3} initial NO 2x10^{-}^{3} initial rate 6.3x10^{-}^{3
}2) initial O_{2} 2x10^{-3} initial NO 1x10^{-3}^{} ^{ } initial rate 2.8x10^{-3} 3) initial O_{2} 1x10^{-3} initial NO 1x10^{-3}^{
} initial rate 7x10^{-4} use this data to calculate the order with respect to NO and NO_{2} and hence determine the overall rate equation and calculate a value for K and give its units .
rate = k[O_{2}]^{2}[NO]
7x10^{-4}/(1x10^{-3})^{2} = k = 700mol^{-1}dm^{3}s^{-1}