Chemistry 9701 · AS & A Level · Atoms, molecules and stoichiometry

Atoms, molecules and stoichiometry — practice question

Because fossil fuels are expected to become progressively scarcer in the future, a range of compounds is being explored for use in internal combustion engines. One example is DME or dimethyl ether, $\text{CH}_3\text{OCH}_3$. DME is a gas that can be produced from methanol. Methanol can come from biomass, including agricultural plant waste.
(a)[3]

Define, using an equation that includes state symbols, the standard enthalpy change of combustion, $\Delta H_c^{\circ}$, for DME at $298\text{ K}$.

(b)[3]

Use the enthalpy changes of formation, $\Delta H_f^{\circ}$, that are given to calculate $\Delta H_{\text{reaction}}^{\circ}$ for making DME with the equation $2\text{CH}_3\text{OH}(l) \rightarrow \text{CH}_3\text{OCH}_3(g) + \text{H}_2\text{O}(l)$. Include a sign in your answer.

(c(i))

Draw the displayed formula of DME and ethanol.

(c(ii))[2]

What type of isomerism do DME and ethanol show?

(d(i))

Which intermolecular force exists between ethanol molecules, which causes ethanol to be a liquid at room temperature?

(d(ii))[4]

Draw a diagram that clearly shows this intermolecular force. Your diagram should show any lone pairs or dipoles that you think are important. You should include at least two molecules in your diagram.

Worked solution & mark scheme

This 12-mark question has a full step-by-step worked solution and mark scheme. One marking point: “$\mathrm{CH_3OCH_3(l) + 3O_2(g) \rightarrow 2CO_2(g) + 3H_2O(l)}$” …

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