Energy Changes in Chemical and Physical Processes
Energetics · Energy Changes
Syllabus tag: KCSE | Chemistry | Form 4 | Topic 19 Energy Changes
Lesson objectives
By the end of this topic, you should be able to:
- Distinguish exothermic from endothermic changes and draw energy level diagrams.
- Define the standard enthalpy changes and use the correct sign convention.
- Calculate enthalpy changes from experimental data and from bond energies.
- Apply Hess's law and describe fuels and their choice.
Summary
| Heat | Temperature | ΔH | |
|---|---|---|---|
| Exothermic | gives out | rises | negative |
| Endothermic | takes in | falls | positive |
Heat changes are calculated from:
ΔH = mcΔT
Hess's law allows any route to be used between the same start and finish.