Energetics I

Excess zinc was added to 25.0 cm³ of 0.200 mol dm⁻³ copper(II) sulfate. The temperature rose by 10.4 °C. Calculate ΔH for Zn + Cu²⁺ → Zn²⁺ + Cu. (Specific heat capacity of the solution = 4.18 J g⁻¹ °C⁻¹; density of the solution = 1.00 g cm⁻³.)

A spirit burner containing propan-1-ol heated 100 g of water from 20.5 °C to 45.0 °C. The burner lost 0.62 g. Calculate the enthalpy of combustion of propan-1-ol (Mᵣ 60.0) and explain why the value is much less exothermic than the data-book value (−2021 kJ mol⁻¹).

Suggest three improvements to the apparatus.

For N₂O₄(g) → 2NO₂(g), ΔH = +58 kJ mol⁻¹ and ΔS(system) = +176 J K⁻¹ mol⁻¹. Calculate the temperature above which the reaction is feasible and explain why a gas-phase dissociation has a positive entropy change.

The enthalpy change for 2NaHCO₃(s) → Na₂CO₃(s) + H₂O(l) + CO₂(g) cannot be measured directly. A student measured: Na₂CO₃(s) + 2HCl(aq) → 2NaCl(aq) + H₂O(l) + CO₂(g) ΔH₁ = −35.6 kJ mol⁻¹ NaHCO₃(s) + HCl(aq) → NaCl(aq) + H₂O(l) + CO₂(g) ΔH₂ = +27.8 kJ mol⁻¹ Use a Hess cycle to calculate the enthalpy change for the decomposition, and explain why it cannot be measured directly.