3.1.6 Chemical equilibria, Le Chatelier's principle and Kc

Question 1

What is the definition of dynamic equilibrium?

Answer 1

The rates of the forward and reverse reactions are the same.
The net concentrations of the reactants and products of the reaction mixture remain constant.
In a closed system.

Question 2

What is Le Chatelier’s principle?

Answer 2

If a factor affecting the position of equilibrium is altered, the position of the equilibrium shifts to oppose the effect of change.

Question 3

What is Le Chatelier’s principle used for?

Answer 3

Le Chatelier’s principle can be used to predict the effects of changes in temperature, pressure and concentration on the position of equilibrium in homogeneous reactions.

Question 4

What is the effect of increasing the temperature of a reversible reaction?

Answer 4

It favours the endothermic side.

Question 5

What is the effect of increasing the pressure of a reversible reaction?

Answer 5

It favours the side with the least gaseous moles.

Question 6

What is the effect of increasing the concentration of one side of a reversible reaction?

Answer 6

It favours the other side.

Question 7

What happens if you increase the temperature of a reversible reaction that’s endothermic in the forward direction? [3 marks]

Answer 7

(Increasing) the (temperature) shifts the equilibrium to the (RHS)
This is because the equilibrium shifts to oppose the (increase) in (temperature)
Increasing the temperature favours the endothermic reaction.

Question 8

What is the effect of adding a catalyst to a reversible reaction?

Answer 8

It has no effect it just increases the speed at which the reaction reaches equilibrium. The rate of both the forwards and the backward reaction are increased by the same amount.

Question 9

What is Kc?

Answer 9

The ratio between the concentrations of reactants and products in a reversible reaction.
It is not affected by changes in concentration or the addition of a catalyst.
It can only be affected by temperature.