Topic 17.1: Equilbrium

Question 1

Function of Equilibrium Law

Answer 1

a) Find the value of the equilibrium constant

b) Find the value of an unknown equilibrium constant

Question 2

ICE Table

Answer 2

Organized method to track which quantities are knwon and which need to be calculated.

a) Initial concentration
b) Change in concentration from the initial state to equilibrium
c) Equilibrium concentration

Question 3

What happens if a system at equilibrium is subjected to a change in concentration?

Answer 3

a) The system will no longer be at equilibrium

b) Reaction will proceed in one direction or the other until the value Q = Kc

Question 4

Le Chatelier’s principle / Rate law (Explanation)

a) Concentration

Answer 4

a) Increasing the concentration of reactants increases the rate of the forward reaction and so shifts the equilibrium to the right.
b) The value of the equilbirium constant stays constant because concentration changes do not affect the values of the rate constants.

Question 5

Le Chatelier’s principle / Rate law (Explanation)

b) Catalyst

Answer 5

Adding a catalyst increases the values of k and k- by the same factor so the ratio of their values, the equilibrium constant is not affected

Question 6

Le Chatelier’s principle / Rate law (Explanation)

c) Temperature

Answer 6

a) The Arrhenius equation indicates that the rate constant increases with increasing temperature
b) Ea of the forward and backward reactions are different, so their rate constants are differently affected by temperature.
c) For an endothermic reaction, in which Ea (forward reaction) > Ea (backward reaction), the increase in temperature has a greater effect on increasing k than k , so Kc increases as temperature increases.

Question 7

Definition of ∆G (Gibbs free energy change)

Answer 7

Measure of the work that is available from a system

Question 8

If the free energy always decreases in any spontaneous process at constant temperature and pressure, then…

a) ∆G < 0
b) ∆G = 0
c) ∆G > 0

Answer 8

a) The reaction is spontaneous in the forward direction
b) The reaction is at equilibrium
c) The reaction in the forward direction is non-spontaneous (Work must be done to make it occur)

Question 9

When does equilibrium occur in thermodynamic terms?

Answer 9

When the reaction is at a minimum value of Gibbs free energy and a maximum value of entropy

Question 10

Explanation of Gibbs free energy and equilibrium

Answer 10

a) As the reaction progresses, there is a decrease in the total free energy as work is done by the system
b) Because the free energy decreases in both directions, the reaction must go through a composition which corresponds to the minimum value of free energy.
c) The system reaches equilibrium when the total free energies of reactants and products are equal.
d) The decrease in free energy during the reaction appears as work done by the system or as an increase in the entropy.
e) The system has the highest possible value of entropy when free energy is at minimum.

Question 11

Formula that expresses the relationship for Gibbs free energy change and Kc

Answer 11

∆G = - RT ln⁡K