ConceptConceptDocsDocuments

CAIE A-Level Chemistry 5.1.7 Enthalpy Changes from Experiments

Practise using calorimetry data to calculate heat transfer and molar enthalpy while evaluating systematic energy losses.

Syllabus
2028–2030
Course
Chemistry 9701
Level
AS

Exam points

  • calculate q=mcΔT using the heated mass, appropriate specific heat capacity and temperature change
  • divide by moles of the defined reacting substance and reverse the sign for the reaction enthalpy
  • evaluate heat loss, incomplete combustion, evaporation and neglected apparatus heat capacity as error sources

5.1.7—Enthalpy changes from appropriate experimental question 1

[Maximum number: 3]

A neutralisation reaction occurs when NaOH(aq) is added to H2SO4(aq)\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}). equation 1

2NaOH(aq)+H2SO4(aq)→Na2SO4(aq)+2H2O(I)2 \mathrm{NaOH}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \rightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{I})

In an experiment, 50.0 cm350.0 \mathrm{~cm}^{3} of 2.00 moldm−3NaOH(aq)2.00 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{NaOH}(\mathrm{aq}) is added to 60.0 cm360.0 \mathrm{~cm}^{3} of 1.00moldm−3H2SO4(aq)1.00 \mathrm{moldm}^{-3} \mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) in a polystyrene cup and stirred. Both solutions have a temperature of 21.4∘C21.4^{\circ} \mathrm{C} before mixing. The maximum temperature of the mixture is measured.

Calculate the theoretical maximum temperature of the mixture in this experiment.

Assume that:
- enthalpy change of neutralisation, ΔHneut \Delta H_{\text {neut }}, of NaOH(aq) and H2SO4(aq)\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) is −57.1 kJ mol−1-57.1 \mathrm{~kJ} \mathrm{~mol}^{-1}
- full dissociation of H2SO4(aq)\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) occurs
- the specific heat capacity of the final solution is 4.18 J g−1 K−14.18 \mathrm{~J} \mathrm{~g}^{-1} \mathrm{~K}^{-1}
- 1.00 cm31.00 \mathrm{~cm}^{3} of the final solution has a mass of 1.00 g
- there is no heat loss to the surroundings
- the experiment takes place at constant pressure.

Show your working.
theoretical maximum temperature = .............................. ∘C{ }^{\circ} \mathrm{C}

All question bank results loaded