Effect of Concentration and Pressure on Reaction Rate
Specification Reference Physical Chemistry, Kinetics 3.1.5.4
Quick Notes
- Increasing concentration (in solutions) or pressure (in gases) increases reaction:
- More reactant particles per unit volume gives an increase in frequency of collisions.
- Collision theory explains that a higher frequency of collisions leads to more successful reactions per second.
Full Notes
How Concentration and Pressure Affect Reaction Rate
Higher concentration (for solutions) means there are more reactant particles per unit volume.
Equally, a higher pressure (for gases) means particles are forced closer together, increasing collision frequency.
A greater number of collisions per second also means an increase in the rate of successful collisions, giving a faster reaction rate.
Matt’s exam tip
Remember – changing concentration does not alter the proportion of collisions that are successful; this is determined by temperature. Increasing concentration simply raises the total number of collisions per second. Since the success ratio stays the same, a higher total number of collisions means a higher number of successful collisions overall.
Collision Theory and Reaction Rate
According to collision theory:
- Particles must collide with energy ≥ activation energy (Ea) to react.
- Higher concentration/pressure increases collision frequency, leading to more successful collisions per second.
Summary
| Factor | Effect on Rate | Explanation |
|---|---|---|
| Higher Concentration | Increases | More particles per unit volume → More collisions |
| Higher Pressure (Gases) | Increases | Particles are closer together → More collisions |
- Increasing concentration in solutions or pressure in gases increases reaction rate.
- Particles are closer together, so collisions occur more frequently.