Enthalpy changes, calorimetry and fuels

Learning objectives

Classify a reaction as exothermic or endothermic from the sign of the enthalpy change, sketch and label an energy profile showing reactants, products, activation energy and ΔH, and relate the sign to the bonds broken and formed

State the standard conditions used for enthalpy data (100 kPa and a stated temperature, usually 298 K) and define the standard enthalpy changes of reaction, combustion, formation and neutralisation

Calculate the heat transferred in a calorimetry experiment from q = mcΔT, convert it to a molar enthalpy change using ΔH = −q/n, and identify the assumptions and the main sources of error in a simple calorimeter

Analyse a temperature–time graph from a calorimetry experiment by extrapolating the cooling curve back to the time of mixing to correct for heat loss

Write equations for the complete and incomplete combustion of alkanes and alcohols, identify carbon monoxide and carbon as products of incomplete combustion, and compare fossil fuels with biofuels in terms of carbon dioxide released and renewability

Compare fuels using specific energy in J g⁻¹ and energy density in J cm⁻³, and write the electrode half-equations for a hydrogen–oxygen fuel cell under acidic and under alkaline conditions