IB Chemistry HL 1.4.3 Spontaneity Question Bank

Practise IB Chemistry HL 1.4.3 by applying spontaneity to exam-style questions.

Exam points

identify the relevant chemical structure, process or evidence
apply the correct chemical model or equation
evaluate the result using chemical reasoning and data

[Maximum number: 2]

Nitrous acid, $\mathrm{HNO}_{2}$ , is a weak acid which can be used to make acidic buffers.

The overall reaction for the synthesis of ethyl ethanoate from ethane is:

2 \mathrm{C}_{2} \mathrm{H}_{6}(\mathrm{~g})+\mathrm{Cl}_{2}(\mathrm{~g})+\frac{3}{2} \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{C}_{4} \mathrm{H}_{8} \mathrm{O}_{2}(\mathrm{~g})+2 \mathrm{HCl}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{~g})

Explain the effect, if any, on the spontaneity of this reaction if the temperature was increased. Use section 1 of the data booklet.

the $-\mathrm{T} \Delta S$ expression becomes more negative / so Gibbs energy/ $\Delta \mathrm{G}$ becomes more negative

increase in spontaneity «as temperature is increased»

Marking guidance:

Accept feasibility in place of spontaneity.

If $-10 \mathrm{~J} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}$ is used, the answer will be opposite (decrease in spontaneity, -TAS becomes more positive, $\Delta G$ becomes less negative).

Do not accept "spontaneous" without reference to increases.

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1.4.3 (HL)—Spontaneity question 1