There are five main factors that affect the rate of reaction. Each works by changing either the frequency or energy of collisions.
1. Temperature
Higher T → particles move faster → more frequent collisions AND more particles with E ≥ Ea.
~10°C rise ≈ doubles rate
2. Concentration
Higher concentration → more particles per volume → more frequent collisions.
For gases: higher pressure = same effect
3. Surface Area
Smaller pieces → more surface exposed → more collisions with reactant particles.
Only for heterogeneous reactions
4. Catalyst
Provides an alternative pathway with lower Ea. More particles can exceed the lower Ea.
Unchanged at end of reaction
Effect of a Catalyst on Activation Energy
The catalyst lowers the activation energy but does not change ΔH.
Think About It
If a catalyst lowers Ea, how does the Maxwell-Boltzmann diagram change?
The distribution itself does NOT change — the particles still have the same energies. But the Ea line moves to the left, so a larger proportion of particles now has sufficient energy to react.