Rate of Reaction
Quick Notes
- Rate of reaction is the change in concentration of a reactant or product per unit time.
- Collision theory: particles must collide with sufficient energy (activation energy, Ea) for a reaction to occur.
- Most collisions between reactant particles don’t lead to a reaction (they don’t occur with enough energy)
Full Notes
Collision theory and activation energy has been outlined with more background theory
here.
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Definition of Rate of Reaction
The rate of reaction measures how quickly reactants are converted into products. It is calculated as:
Rate of reaction = Change in concentration ÷ Time
Rate = Δ[Reactant or Product] ÷ Δt
Units: mol dm−3 s−1
Collision Theory and Activation Energy
According to collision theory, for a reaction to occur:
- Reactant particles must collide.
- Collisions must have sufficient energy (≥ activation energy, Ea).
- (Particles must also be correctly oriented however this is covered in more detail later in the course - see Rate Equations.)
If collision energy is less than the required activation energy (Ea), the reaction does not occur. Increasing temperature, concentration, surface area, or adding a catalyst increases the number of successful collisions per second, speeding up the reaction.
Factors Affecting Rate of Reaction
There are several factors that can affect the rate of a reaction – these are covered in more detail in following topics (1.5.3, 1.5.4 and 1.5.5).
| Factor | Effect on Rate | Explanation |
|---|---|---|
| Concentration | Increases | More frequent collisions |
| Temperature | Increases | More particles have E ≥ Ea |
| Surface Area | Increases | More exposed particles for collisions |
| Catalyst | Increases | Provides an alternative reaction pathway with lower Ea |
Summary
- Rate of reaction = Δ[Concentration] ÷ Δt (mol dm−3 s−1).
- Collision theory: successful collisions require energy ≥ Ea.
- Factors affecting rate: concentration, temperature, surface area, and catalysts.