IB Chemistry HL 1.2.3 Standard enthalpy changes Question Bank

Practise IB Chemistry HL 1.2.3 by applying standard enthalpy changes 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: 1]

Phosphoryl chloride, $\mathrm{POCl}_{3}$ , is a dehydrating agent.

$\quad \mathrm{POCl}_{3}(\mathrm{~g})$ decomposes according to the following equation.

2 \mathrm{POCl}_{3}(\mathrm{~g}) \rightarrow 2 \mathrm{PCl}_{3}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g})

Define the term standard enthalpy change of formation, $\Delta H_{\mathrm{f}}{ }^{\ominus}$ .

heat/enthalpy change/required/absorbed when 1 mol of a compound is formed from its elements in their standard states/at $100 \mathrm{kPa} / 10^{5} \mathrm{~Pa} / \mathrm{l} \mathrm{bar}$ ; Allow $1.01 \times 10^{5} \mathrm{~Pa} / 101 \mathrm{kPa} / 1 \mathrm{~atm}$ .

Marking guidance:

Allow under standard conditions or standard temperature and pressure.
Temperatures not required in definition, allow if quoted (for example, $298 \mathrm{~K} / 25^{\circ} \mathrm{C}$ - most common) but pressure value must be correct if stated.

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1.2.3 (HL)—Standard enthalpy changes question 1