Chemistry 0620 · IGCSE · Exothermic and endothermic reactions

Exothermic and endothermic reactions — practice question

Chemical reactions may involve a transfer of thermal energy.
(a)[1]

State the name of the term for the transfer of thermal energy during a reaction.

(b(i))[3]

State what happens, if anything, to the forward reaction rate when the concentration of $\text{CCl}_4$ is increased. Explain your answer with collision theory.

(b(ii))[2]

State what happens to the equilibrium position, if anything, when pressure is increased. Explain your answer.

(b(iii))[3]

On Fig. 5.1: • add the formulae of the reactants and products • include an arrow, labelled $E_a$, to indicate the activation energy • include an arrow, labelled $\Delta H$, to show the transfer of energy in the reaction.

(b(iv))[2]

Define the term activation energy.

(b(v))[1]

State one way in which the activation energy of a reaction can be changed.

(c)[4]

Use the bond energies in Table 5.1 together with the $\Delta H$ value for the reaction to work out the H-Cl bond energy by following these steps: • Work out the energy needed to break the bonds in the reactants. • Work out the energy released when the bonds in carbon dioxide are formed. • Work out the H-Cl bond energy.

Worked solution & mark scheme

This 16-mark question has a full step-by-step worked solution and mark scheme. One marking point: the enthalpy change of reaction

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