Quick answer: Thermochemistry measures heat changes in reactions. This AP Chemistry test on thermochemistry has 8 questions worth 20 marks, to do in 45 minutes: reading the sign, calorimetry and Hess’s law. The mark scheme is on a separate page; free printable PDF.
This test lasts 45 minutes and covers heat flow, calorimetry, Hess’s law, formation enthalpies and bond enthalpies. A calculator is allowed. Use 4.18 J/(g °C) for water. Show all working; the total is 20 marks.
Level: AP Chemistry · Curriculum: AP Chem Unit 6
Question 1 Reading the sign (2 marks)
A cold pack contains NH₄NO₃. When it dissolves, the temperature falls. State whether the process is exothermic or endothermic, and give the sign of ΔH.Question 2 Calorimetry (3 marks)
In a calorimeter, 150.0 g of water rises from 18.0 °C to 31.5 °C when 0.0400 mol of a reagent reacts completely (c = 4.18 J/(g °C)).- Calculate q. (2 marks)
- Calculate ΔH in kJ/mol. (1 mark)
Question 3 Hess’s law (3 marks)
(1) 2 C(s) + O₂(g) → 2 CO(g), ΔH = −221 kJ. (2) 2 CO(g) + O₂(g) → 2 CO₂(g), ΔH = −566 kJ. Calculate ΔH for C(s) + O₂(g) → CO₂(g).Question 4 Formation enthalpies (3 marks)
4 NH₃(g) + 5 O₂(g) → 4 NO(g) + 6 H₂O(g). ΔH°f (kJ/mol): NH₃ −45.9, NO +90.3, H₂O(g) −241.8. Calculate ΔH°.Question 5 Bond enthalpies (3 marks)
CH₄(g) + Cl₂(g) → CH₃Cl(g) + HCl(g). Bond enthalpies (kJ/mol): C–H 413, Cl–Cl 243, C–Cl 339, H–Cl 432. Estimate ΔH.Question 6 Heat loss (2 marks)
A student’s calorimetry result for a neutralisation is −53 kJ/mol, while the accepted value is −57 kJ/mol. Explain why heat loss would give a result like this.Question 7 Enthalpy levels (2 marks)
- State ΔH for A → C. (1 mark)
- State ΔH for C → B. (1 mark)
Question 8 Specific heat capacity (2 marks)
A 45.0 g metal sample at 100.0 °C is dropped into 100.0 g of water at 20.0 °C. The final temperature is 23.5 °C. Assuming no heat loss, calculate the specific heat capacity of the metal.
