ChemistryCode 9701
Enthalpy change, ΔH
What this topic asks you to be able to do
- understand that enthalpy changes take place alongside chemical reactions, and that a change may be exothermic, with ΔH negative, or endothermic, with ΔH positive
- construct and interpret a reaction pathway diagram with regard to the reaction's enthalpy change and its activation energy
- define and apply the following terms: (a) standard conditions, taken as 298K and 101kPa and marked by ⦵; (b) enthalpy change, particularly in relation to: reaction, ΔHr, formation, ΔHf, combustion, ΔHc, neutralisation, ΔHneut
- appreciate that energy is exchanged in chemical reactions as a result of bonds being broken and formed
- apply bond energies (with ΔH positive, i.e. for bond breaking) in working out the enthalpy change of reaction, ΔHr
- understand that a bond energy is in some cases exact and in other cases an average
- work out enthalpy changes from suitable experimental data, including applying the relationships q = mcΔT and ΔH = –mcΔT/n