Unit 7
Rates and energy changes.
Why reactions are fast or slow: collisions, temperature, the activation barrier and catalysts, and the heat they give out or take in.
Before this unit
- Reactions and equations
- Energy Physics
The unit, lesson by lesson
Lessons
4 lessons · 22 practice questions · about 2 hours
Collision theory
Why only some collisions lead to a reaction, why twice the concentration makes it four times faster, and why a hundred degrees speed it up far more than the molecules' speed suggests.
Activation energy and catalysts
The hump every reaction has to get over, and how a catalyst opens a lower route without giving any energy and without running out: the platinum in a catalytic converter.
Exothermic and endothermic
Where the energy in a reaction goes: burning that gives out heat, the power of a flame, the sign of ΔH, and a cold pack that takes heat in from your hand.
Bond energies
Where a flame's heat comes from: breaking bonds takes energy in and making them gives it out, and working out the ΔH of burning from a table of bond energies.