IB Chemistry R2.2 R2.2.1

Rate of Reaction

Defining reaction rate, experimental methods for monitoring change, and calculating rates from graphs.

Reactivity 2.2 SL & HL ⏱️ ~5 min revision

For a reaction to occur, particles must collide with sufficient energy (≥ activation energy, Ea) and correct orientation.

Core Definition

Definition and Formula of Reaction Rate

\( \text{Rate} = \dfrac{\Delta [\text{concentration}]}{\Delta t} \)

Units: \(\text{mol dm}^{-3}\text{ s}^{-1}\) (or \(\text{g s}^{-1}\), \(\text{cm}^3\text{ s}^{-1}\)). Rate is always expressed as a positive quantity.

Maxwell-Boltzmann Distribution

Diagram: Maxwell-Boltzmann Distribution Kinetic Energy → Number of particles Lower T Higher T Ea Particles with E ≥ Eₐ can react

At higher temperature, the distribution shifts right and flattens - more particles have E ≥ Ea.

Conceptual Check

Area Under Maxwell-Boltzmann Distribution Curves

The total area under a Maxwell-Boltzmann distribution curve represents the total number of particles in the sample. Heating a sample increases particle speeds but does not change the total number of particles; hence the area remains strictly constant while the peak shifts right and down.

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