Thermochemistry is about the energy exchanged with the surroundings during a reaction. It has three parts that depend on each other: the meaning of the terms, the diagrams, and the calculations.
This page sits under SPM Chemistry. It shows the order to study, one short example, and where to begin.
How do the lessons connect?
The vocabulary decides the sign and the diagram, and the diagram decides how you read the numbers.
- Distinguishing exothermic and endothermic changes sets the meaning.
- Reading energy-level diagrams turns the meaning into a picture.
- Calculating heat change from experimental data puts numbers to it.
- Explaining sign conventions and sources of error refines your answers.
- Energy evidence and industrial chemistry reasoning practises reasoning from supplied data.
What does one example look like?
An original experiment: 50 cm³ of water in a polystyrene cup rises from 28.0 °C to 34.5 °C when a solid dissolves.
The temperature of the surroundings rose, so the change released heat: it is exothermic, and ΔH is negative. On an energy-level diagram the products sit below the reactants.
For the number, Q = mcθ = 50 × 4.2 × 6.5 = 1 365 J. Dividing by the moles dissolved gives ΔH per mole, which the calculation lesson shows step by step.
Who should start where?
- You mix up which change is which: start with the first lesson.
- You can name the change but diagrams confuse you: start with energy-level diagrams.
- You understand diagrams but lose marks on calculations: start with the heat change lesson.
- You can do all the above but unfamiliar data stumps you: try the energy evidence section.
Activation energy, which shares a diagram with this chapter, is covered in rate of reaction. Finish with the thermochemistry practice set.
Need a teacher to check where you stand?
A teacher can ask one question from each part and find the gap in a few minutes. If you would like that, see online one-to-one Chemistry tuition and the one-hour trial class (from RM50).