CalorimetryEdexcel International A Level Chemistry: Mind map

Exam questions on Calorimetry

1. A student measures the enthalpy change of neutralisation. She mixes 50.0 cm³ of 1.00 mol dm⁻³ hydrochloric acid with 50.0 cm³ of 1.00 mol dm⁻³ sodium hydroxide solution in a polystyrene cup with a lid, stirring gently. Both solutions start at the same temperature and the highest temperature reached is 6.8 °C higher. Assume that the solution has density 1.00 g cm⁻³ and specific heat capacity 4.18 J g⁻¹ °C⁻¹.
   Calculate the energy transferred to the solution, in J, and state one assumption made in your calculation.2 marks
2. A student determines the standard enthalpy change of combustion of ethanol, C₂H₅OH (Mr = 46.0). She heats 200.0 g of water in a copper can using a spirit burner and measures a rise in temperature of 25.0 °C. The mass of the burner falls by 0.92 g. The specific heat capacity of water is 4.18 J g⁻¹ °C⁻¹. The data-book value for ethanol is –1367 kJ mol⁻¹.
   The experimental value is less exothermic than the data-book value. Suggest two reasons for this.2 marks
3. A student measures the enthalpy change for the reaction Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s). She puts 50.0 cm³ of 0.200 mol dm⁻³ copper(II) sulfate solution in a polystyrene cup and records its temperature every 30 seconds for 2 minutes. At 2.5 minutes she adds an excess of zinc powder (without taking a reading) and carries on recording the temperature every 30 seconds until 8 minutes, stirring throughout. She plots temperature against time.
   Explain why a cooling-curve correction is needed and describe how the student uses her graph to find the correct temperature change.3 marks