Chemistry › Section E · Thermochemistry › Topic E.3
Enthalpy and Hess's law
Most reactions happen in open containers at constant pressure, and the heat they exchange there has its own name: the enthalpy change, ΔH. Because enthalpy depends only on where a reaction starts and ends, you can add known reactions together to find the ΔH of reactions nobody can measure directly.
In this topic
- Internal energy and the first law
- State functions
- Enthalpy: heat at constant pressure
- Thermochemical equations
- Standard enthalpies of combustion and formation
- Worked example: burning methane
- Hess's law
- Worked example: Hess's law in sulfuric acid manufacture
- Enthalpies of reaction from formation values
- Worked example: the thermite reaction
- Common mistakes to avoid
- Key takeaways
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