Chemistry 9701 · AS & A Level · Hydrocarbons

Hydrocarbons — practice question

$\text{C}_3\text{H}_6$ reacts with HBr(g) in an addition reaction.
(a(i))[1]

What is meant by an addition reaction?

(a(ii))[4]

Complete Fig. 3.1 to show the mechanism for the addition reaction of $\text{C}_3\text{H}_6$ with HBr that forms 2-bromopropane. Show charges, dipoles, lone pairs of electrons and curly arrows where needed.

(a(iii))[2]

Explain why 2-bromopropane is formed in greater amount than 1-bromopropane in this reaction.

(b(i))[1]

$\mathrm{H_2(g)}$ and nickel are added to alkene X. Fig. 3.2 shows the way the concentration of X varies with time. Use Fig. 3.2 to identify the limiting reagent in this reaction. Explain your answer.

(b(ii))[1]

Use Fig. 3.2 to describe how the gradient changes as the reaction proceeds. State what this indicates about the rate during this reaction.

(c)[2]

Use Table 3.1 to calculate the enthalpy change per mole of $\text{C}_6\text{H}_{14}$ formed in this reaction.

(d(i))[1]

Annotate Fig. 3.3 to show the effect of adding nickel to Y and $\mathrm{H_2}(g)$ at temperature $T$.

(d(ii))[2]

Area $B$ (not labelled on Fig. 3.3) shows the number of molecules with energy greater than or equal to the activation energy when nickel is added at temperature $T$. State the difference, if any, between areas A and B. Explain the importance of your answer for the rate of hydrogenation of Y. Give your answer in terms of collisions.

(e)[2]

Suggest the structure of Z.

Worked solution & mark scheme

This 16-mark question has a full step-by-step worked solution and mark scheme. One marking point: Two or more reactants join to form just one product

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