Which of the following statements best describes an exothermic reaction?

A. Energy is absorbed from the surroundings.

B. The products have higher potential energy than the reactants.

C. Energy is released to the surroundings.

D. The activation energy is zero.

What is the significance of activation energy in a chemical reaction?

A. It is the energy required to break the bonds in the reactants.

B. It is the energy difference between the reactants and products.

C. It is the minimum energy required for a reaction to occur.

D. It is the energy released during the reaction.

Which of the following factors does NOT affect the activation energy of a reaction?

A. Temperature

B. Concentration of reactants

C. Presence of a catalyst

D. Nature of reactants

How does a catalyst affect the activation energy of a reaction?

A. Increases the activation energy

B. Decreases the activation energy

C. Does not change the activation energy

D. Makes the activation energy zero

In a potential energy diagram, how can one distinguish between an exothermic and an endothermic reaction?

A. In exothermic reactions, the products are at a higher energy level than the reactants.

B. In endothermic reactions, the products are at a lower energy level than the reactants.

C. In exothermic reactions, the products are at a lower energy level than the reactants.

D. Both A and B are correct.

a) Explain the difference between exothermic and endothermic reactions in terms of energy changes. [2]

b) Given that a reaction has a positive enthalpy change, classify it as exothermic or endothermic. Justify your answer. [2]

a) Describe the significance of activation energy in a chemical reaction. [2]

b) How does the presence of a catalyst affect the activation energy of a reaction? [2]

a) Using a potential energy diagram, describe the energy changes that occur during an exothermic reaction. [2]

b) In the context of a potential energy diagram, explain the term "energy barrier" for a reaction. [2]

a) Define the term "enthalpy change" in the context of chemical reactions. [2]

b) How is the enthalpy change of a reaction related to the bond energies of the reactants and products? [2]

c) Why might the actual enthalpy change of a reaction in a laboratory differ from the theoretical value? [3]

a) Describe the role of a catalyst in a chemical reaction. [2]

b) How does a catalyst affect the rate of both exothermic and endothermic reactions? [3]

c) Explain why a catalyst does not alter the equilibrium position of a reversible reaction. [2]