Chemistry (AS Level)·Chemical energetics · NSSCAS 2.1.1
Enthalpy changes
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Every reaction absorbs or releases energy. Learn the enthalpy change ΔH and its sign, the standard enthalpy changes chemists define, how to measure ΔH with calorimetry (ΔH = −mcΔT), and how to calculate it from bond energies — and why the two methods don't always agree.
What you'll learn in this lesson
By the end you should be able to (NSSCAS Chemistry (AS Level) 2.1.1):
- Explain that reactions are accompanied by energy changes: exothermic (ΔH negative) and endothermic (ΔH positive)
- Explain and use enthalpy change of reaction and standard conditions, and the standard enthalpy changes: formation, combustion, hydration, solution, neutralisation, atomisation
- Explain bond energy (ΔH positive for bond breaking)
- Calculate enthalpy changes from experimental results using ΔH = −mcΔT
- Calculate energy changes using bond energies, and explain why these differ from data-booklet and experimental values
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