Deck 5: equilibria

Question 1

definition of dynamic equilibrium

Answer 1

dynamic equilibrium is a state in a reversible reaction within a closed system in which the forward and backwards reactions are continuing at the same rate, resulting in no net change in macroscopic properties (eg. concentration, partial pressure) of the reactants and products

Question 2

graphs to represent equilibrium conc time and rate time

Answer 2

check notes (one for concentration, mol dm-3, one for rate of reaction, mol dm-3 s-1)

Question 3

LCP definition

Answer 3

when a system in equilibrium is subjected to a change, the system will react to counteract the change imposed so as to reestablish the equilibrium

Question 3

what is Qc and Kc

Answer 3

at any given time, the reaction quotient Qc is the ratio of the concentrations of reactants and products raised to their stoichiometric ratios

Qc = [C]^c[D]^d/[A]^a[B]^b

K is a measure of the extent of reaction

at equilibrium, Qc becomes constant and this value is Kc (ONLY DEPENDENT ON TEMP)

Question 3

How is Kp different from Kc

Answer 3

Kc use conc and Kp use partial pressure

Question 4

what is kf and kb
relationship between Kf and Kb and Kc

Answer 4

Kf is rate constant of rate of forward rxn
ratef= Kf[A]^a[B]^b

Kb is rate constant of rate of backwards reaction

Kc = Kf/Kb = [C]^c[D]^d/[A]^a[B]^b

Question 5

what is the overall Kc for reaction with multiple smaller reactions

Answer 5

product of Kc for each reaction

Question 6

Kc for reaction where the stoichiometric coefficients of a balanced equation are multiplied by a factor n

Answer 6

new Kc = K^n

Question 7

when can water be excluded from the eqm constant

Answer 7

when water is used as a solvent (eg. in a reaction in aqueous medium and water is a reactant, conc of water can be taken to be approx. constant as it is present in large amounts)

Question 8

definition of degree of dissociation

Answer 8

the fraction of reactant that has dissociated at a particular temperature

Question 9

homo vs hetero eqm

Answer 9

homo: eqm system in which all the substances involved are in the same phase

hetero: eqam system in which the substances are not in the same phase

Question 10

what can be included for Kc and Kp of hetero eqm

Answer 10

conc/partial pressure of pure solids and liquids as they are constant at a constant temp

conc of water when it is present in large amounts in an aqueous solution

Question 11

ΔG at eqm

Answer 11

ΔG = 0

Question 12

formula for ΔG relating K and what its signs mean

Answer 12

ΔG⦵ = -RT ln K

when ΔG⦵<0, K >1 and poe lies more right

when ΔG⦵ > 0, K <1 and poe lies more left

Question 13

just read

Answer 13

collision theory for LCP

eg. if u add more reactant, frequency of effective collisions between reactants increase and rate of forward reaction increases where rate of forward > rate of backward until eqm is reestablished

Question 14

think about LCP change in conc graph

Answer 14

refer to notes if needed

Question 14

think about LCP change in TOTAL pressure graph

Answer 14

refer to notes if needed
rmb all partial pressures increase at the start

Question 15

effect of change in volume on rate of reaction

Answer 15

when V increases, partial pressure of all gases decrease and since p is proportionate to concentration, concentration decreases and rate of both forward and backward reactions decrease

takes longer to reach eqm

Question 16

effect of change in temperature on rate of reaction

Answer 16

when temp increases, the rate constants of both the forward and backward reaction increases as

k=Ae^-Ea/RT

the particles with energy greater than or equal to activation energy Ea increases and time to reach eqm decreases

Question 17

addition of catalyst on eqm

Answer 17

lower activation energy of both forward and backward reaction to the same extent hence rate for both forward and backward reaction increased by the same extent and adding catalyst has no effect on eqm constant k and the composition of the eqm mixture

but eqm is reached more quickly

Question 18

what is the haber process equation is it exo or endo

Answer 18

N2 + 3H2 reversible arrow 2NH3

exo

Question 19

conditions for haber process

Answer 19

1. moderately high temp 450˚C
   - since forward is exo, low temp will lead to higher yield
   - but too slow at low temp
   - but high temp means lower yield and higher cost so compromise made
2. 200atm
   - high pressure favour forward reaction but cost of production increase and dangerous
   - compromise to moderate pressure
3. catalyst of finely divided iron catalyst with aluminium oxide promoter
   - increase production rate and yield not affected
4. continued removal of ammonia
   - shift eqm position to the right and increase yield of ammonia
   - through cooling of reaction to liquefy ammonia
5. keep molar ratio of N2 and H2 to 1:3
   - minimise excess

Question 20

effect of adding inert gas as constant vol or at constant pressure

Answer 20

constant vol
- total pressure increase but partial pressures do not change so no change in K and eqm not affected

constant pressure
- total volume increase
- partial pressures decrease and eqm shift to produce more moles of gas