In a closed system at equilibrium, which of the following statements is true?

A. The concentration of reactants is zero.

B. The rate of the forward reaction is greater than the rate of the reverse reaction.

C. The concentration of products and reactants remains constant.

D. The reaction has completely stopped.

Which of the following is a characteristic of a system at equilibrium?

A. The system is at its lowest energy state.

B. The system no longer reacts with its surroundings.

C. The system's macroscopic properties remain unchanged.

D. The system has reached maximum entropy.

According to Le Chatelier's principle, if the concentration of a reactant in a system at equilibrium is increased, what will happen to the position of equilibrium?

A. It will shift towards the products.

B. It will shift towards the reactants.

C. It will remain unchanged.

D. It will shift in a direction that reduces the change.

In the Haber process for the synthesis of ammonia, how does an increase in pressure affect the position of equilibrium?

A. Shifts to the right, favouring the formation of ammonia.

B. Shifts to the left, favouring the decomposition of ammonia.

C. Remains unchanged.

D. Shifts in a direction that increases the pressure.

For a given reaction at equilibrium, if Kc is much greater than 1, what can be inferred?

A. The concentration of reactants is much higher than that of products.

B. The concentration of products is much higher than that of reactants.

C. The reaction is not at equilibrium.

D. The reaction rate is very slow.

a) Explain the concept of forward and reverse reactions occurring at the same rate in a chemical system. [2]

b) What are the main characteristics of a system that is at equilibrium? [2]

a) Describe the effect of increasing the concentration of a reactant on the position of equilibrium. [2]

b) How does the addition of a catalyst affect the rate of reaching equilibrium? [2]

a) Define the term 'Kc' in the context of chemical equilibrium. [2]

b) How is the value of Kc related to the position of equilibrium in a reaction? [2]

a) Describe the industrial significance of Le Chatelier's principle with respect to the Haber process. [3]

b) In the context of the Haber process, what would be the effect on the equilibrium yield of ammonia if the pressure was increased? [2]

c) Why is a compromise temperature used in the Haber process? [2]

a) Define the term 'half-life' in the context of a first-order reaction. [2]

b) How is the half-life of a first-order reaction related to its rate constant? [2]

c) Why is the half-life of a first-order reaction independent of the initial concentration? [3]