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IB Chemistry HL 1.1.4 Standard Enthalpy Change H Questions

Apply calorimetry equations and mark-scheme conventions to calculate q, determine molar ΔH and compare measured energy changes with experimental limits.

Syllabus
First assessment 2025
Course
Chemistry HL
Level
HL

Exam points

  • Calculate heat transferred at constant pressure with q = mcΔT, using mass, specific heat capacity, temperature change and consistent units.
  • Convert measured heat into molar enthalpy change using amount of substance or stoichiometry, with the correct sign and kJ mol⁻¹ units.
  • Use calorimetry observations, temperature changes and experimental assumptions or heat-loss evidence to compare the energy change of reactions or dissolutions.

IB Chemistry HL 1.1.4 Standard Enthalpy Change H Questions question 1

[Maximum number: 1]

Phosphine (IUPAC name phosphane) is a hydride of phosphorus, with the formula PH3\mathrm{PH}_{3}.

Impurities cause phosphine to ignite spontaneously in air to form an oxide of phosphorus and water.

200.0 g\quad 200.0 \mathrm{~g} of air was heated by the energy from the complete combustion of 1.00 mol phosphine. Calculate the temperature rise using section 1 of the data booklet and the data below.

Standard enthalpy of combustion of phosphine, ΔHc⊖=−750 kJ mol−1\Delta H_{\mathrm{c}}^{\ominus}=-750 \mathrm{~kJ} \mathrm{~mol}^{-1}
Specific heat capacity of air =1.00Jg−1 K−1=1.00 kJ kg−1 K−1=1.00 \mathrm{Jg}^{-1} \mathrm{~K}^{-1}=1.00 \mathrm{~kJ} \mathrm{~kg}^{-1} \mathrm{~K}^{-1}

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