AQA A Level Chemistry - Chemical Equilibria

Question 1

What is a reversible reaction?

Answer 1

• In a reversible reaction, the REACTANTS turn into PRODUCTS and the PRODUCTS can then be turned back into the REACTANTS

Question 2

How is Equilibrium established?

Answer 2

• When an equilibrium reaction starts there are only reactants present
• The reactants are used up as time goes by because the forward reaction occurs
• The rate of the forward reaction decreases as time passes due to the reactants being used up
• When the reaction starts, there are no products but the products are made as time goes by
• The rate of the backward reaction increases as time passes due to the increase in the amount of products
• After a certain amount of time, the forward reaction rate will equal the backward reaction rate
• This means that as the reactants are being used up and turned into products, the products are being used up and being turned into reactants

Question 3

Model Answer: How is a dynamic equilibrium reached?

Answer 3

• At the rate of the reaction the forward reaction is fast and the backward reaction is slow
• After the start, the reverse reaction speeds up as the forward reaction slows down
• The rate of the forward reaction becomes the same as the rate of the backward reaction

Question 4

What does Dynamic Equilibrium mean?

Answer 4

• The forward and backward reactions proceed at equal rates
• The concentration of the reactants and products are constant

Question 5

When can Dynamic Equilibrium occur?

Answer 5

• Dynamic Equilibrium can only occur if the reversible reaction is carried out in a sealed container, so that no products can escape
• This is known as a closed system

Question 6

Model Answer: State Le Chatelier’s principle

Answer 6

• The position of equilibrium will shift to oppose a change made to it

Question 7

What will happen if the concentration of CO is increased?

Answer 7

• The equilibrium will shift to the right
• To oppose the addition of CO (reactant)
• So yield of CO2 and H2 increases

Question 8

What will happen if the concentration of CO is reduced?

Answer 8

• The equilibrium will shift to the left
• To oppose the reduction of CO
• So yield of CO and H2O increases