1.1. A student is investigating chemical reactions that produce heat.

She adds zinc to hydrochloric acid, HCl.

Zinc chloride, ZnCl₂, and hydrogen gas are made.

i) Write the balanced symbol equation for this reaction.

[2]

ii) What term is used to describe a reaction that produces heat?

[1]

1.2. The student draws the reaction profile for this reaction, as shown in Fig. 18.1.

Explain what is meant by the term activation energy.

1.3. Higher Only 

Combustion reactions produce a lot of heat energy.

Bond energies can be used to calculate the energy change in combustion reactions.

Methane is a common fuel used in combustion reactions.

Methane reacts with oxygen. Carbon dioxide and water are made, as shown in Fig. 18.2.

i) The reaction of methane with oxygen produces heat.

Explain why.

Use ideas about bond breaking and bond making in your answer.

[3]

ii) Calculate the total energy transferred to break the bonds in the reactants in Fig. 18.2.

Total energy transferred = ............................................... kJ / mol [1]

iii) Calculate the total energy transferred to make the bonds in the products in Fig. 18.2.

Total energy transferred = ............................................... kJ / mol [1]

iv) Use your answers to parts (ii) and (iii) to calculate the energy change for the reaction in Fig. 18.2.

Energy change = ............................................... kJ / mol [1]