3.2.3 Chemical Equilibrium

Question 1

When does dynamic equilibrium occur?

Answer 1

• in a closed system
• when the rate of the forward reaction is equal to the rate of the reverse reaction
• when the concentrations of the reactants and products do not change
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Question 2

What is the effect of concentration on equilibrium?

Answer 2

• equilibrium will shift to the opposite side where conc is increased

Question 3

What is the effect of pressure on equilibrium?

Answer 3

• increasing pressure favours the reaction which has a decrease in the total number of moles
• decreasing pressure favours the reaction which has an increase in the total number of moles

Question 4

What is the effect of temperature on equilibrium?

Answer 4

• increasing temperature favours the endothermic reaction
• decreasing temperature favours the exothermic reaction
• (using a low temp will mean very slow r of r)

Question 5

What is the effect of a catalyst on equilibrium?

Answer 5

• increases the rate of forward and backward reactions equally
• has no effect on the position of equilibrium
• increases the rate at which equilibrium is established

Question 6

What are the conflicts when designing an industrial process?

Answer 6

• rate of reaction
• equilibrium yield
• improved output of product and increased manufacturing cost

Question 7

What are the compromises on the conditions of the Haber process?

Answer 7

• temperature most be lowest possible temperature at which the reaction can proceed at a reasonable rate, even though equilibrium shifts to the left at high temperature (450°C)
• pressure chosen must be highest possible, modern plants use a pressure of 200atm, to increase the pressure even higher would require even thicker walled steel containers which would be expensive
• a catalyst is essential as the reaction is too slow to give an economical rate of reaction (iron)

Question 8

How to calculate Kc?

Answer 8

Kc = [products]/[reactants]
Products and reactants to the power of their moles
If multiple products or reactants, x them

Question 9

How to see position of equilibrium from Kc?

Answer 9

• when Kc is > 1 there are more products than reactants and equilibrium lies to the right
• when Kc is < 1 there are more reactants than products and equilibrium lies to the left

Question 10

State Le Chatelier’s principle

Answer 10

• if a change is made to a system in dynamic equilibrium the position of equilibrium moves to counteract this change