U3-4-1 - Equilibria

Question 1

At equilibrium, the
_____ of forward and reverse reactions are equal.

Answer 1

rates

Question 2

At equilibrium, the
_____ of forward and reverse reactions are constant.

Answer 2

concentrations

Question 3

State the effect a catalyst has on the equilibrium position

Answer 3

None
(rates of forward/reverse reactions are increased by the same amount)

but equilibrium is reached faster

Question 4

If pressure is increased, which reaction will be favoured:
forward or reverse?

Answer 4

Forward

Question 5

The forward reaction is favoured if pressure is increased.
Why?

Answer 5

Fewer gas moles on product side

so favouring forward reaction helps decrease pressure

Question 6

If pressure is increased, which reaction will be favoured:
forward or reverse?

Answer 6

Reverse

Question 7

Pressure has no effect on this equilibrium. Why?

Answer 7

Same no. of gas moles on both sides

Question 8

Would you increase or decrease temperature to maximise product yield?

Answer 8

Decrease

Reaction is exothermic

Question 9

Would you increase or decrease temperature to maximise product yield?

Answer 9

Increase

Reaction is endothermic

Question 10

Why does an increase in temperature favour reactants?

Answer 10

Reaction is exothermic

(so reverse reaction will be favoured to reduce heat)

Question 11

State Le Chatelier’s principle

Answer 11

If a system at equilibrium is subjected to any change, the system readjusts itself to counteract the applied change.

E.g. increased T = endothermic reaction favoured to lower it again

Question 12

Why does adding OH⁻ ions increase the rate of the reverse reaction?

Answer 12

Because OH⁻ reacts with H⁺, and the reverse reaction is favoured to replace the H⁺ used up

Question 13

Suggest one way to maximise profit in an industrial process.

Answer 13

Any of:
*recycle/sell by-products
*use catalysts
*run reactions at low temperatures if possible
*use cheap feedstocks if possible.