Enthalpy changes and enthalpy level diagramsEdexcel International A Level Chemistry: Mind map

Exam questions on Enthalpy changes and enthalpy level diagrams

1. A food company sells self-heating drink cans. The base of each can holds solid calcium oxide separated from water by a seal. Pulling a tab mixes them: CaO(s) + H₂O(l) → Ca(OH)₂(s), for which ΔH = –65 kJ mol⁻¹ at constant pressure.
   Describe the enthalpy level diagram for this reaction, stating what is on the vertical axis and what the labels and arrow show.2 marks
2. A teacher demonstrates two energy changes. First, ethanol is burned in a spirit burner; the standard enthalpy change of combustion of ethanol is –1367 kJ mol⁻¹. Second, dilute hydrochloric acid is mixed with aqueous sodium hydroxide in an insulated cup; the standard enthalpy change of neutralisation of a strong acid by a strong alkali is –57 kJ mol⁻¹.
   Write the ionic equation, including state symbols, for the neutralisation reaction, and use it to explain why the enthalpy change of neutralisation is almost the same for any strong acid and strong alkali.2 marks
3. A chemist is studying the enthalpy changes of chlorine and its compounds. The standard enthalpy change of atomisation of chlorine is +122 kJ mol⁻¹ and the standard enthalpy change of formation of hydrogen chloride gas is –92 kJ mol⁻¹.
   Define the term standard enthalpy change of atomisation and write the equation for the standard enthalpy change of atomisation of chlorine.3 marks