5.1 Enthalpy change, ΔH

Understand that chemical reactions are accompanied by enthalpy changes, and that these changes can be exothermic (ΔH is negative) or endothermic (ΔH is positive).

Taught in: Reactions that warm you up and cool you down · 6 questions

Construct and interpret a reaction pathway diagram in terms of the enthalpy change of the reaction and the activation energy.

Taught in: Reaction pathway diagrams: the hill between reactants and products · 6 questions

Define and use the terms: (a) standard conditions, shown by ⦵; (b) enthalpy change, with particular reference to reaction, ΔHr, formation, ΔHf, combustion, ΔHc, and neutralisation, ΔHneut.

This syllabus takes standard conditions to be 298 K and 101 kPa.

Taught in: The four enthalpy changes you must define, Standard conditions: the fair-comparison rule · 13 questions

Understand that energy transfers occur during chemical reactions because chemical bonds are broken and made.

Taught in: Bonds: pay to break, get paid to make · 6 questions

Use bond energies (ΔH positive, i.e. bond breaking) to calculate the enthalpy change of reaction, ΔHr.

Taught in: Bond energy calculations, and why the answer is only an estimate · 5 questions

Understand that some bond energies are exact and some bond energies are averages.

Taught in: Bond energy calculations, and why the answer is only an estimate · 2 questions

Calculate enthalpy changes from appropriate experimental results, including the use of the relationships q = mcΔT and ΔH = –mcΔT/n.