IB Chemistry home > Syllabus 2016 > Kinetics > The energy barrier

Syllabus ref: 16.2

Particles need to have a certain minimum energy in order to cause successful collisions. The temperature of a reaction mixture gives a measure of the amount of energy available to the particles.

At a higher temperature the particles on average have higher energy. This translates into particles moving faster and more energetically.

Consequently, collisions are more frequent and occur with greater energy and more successful.

Nature of science:

Theories can be supported or falsified and replaced by new theories-changing the temperature of a reaction has a much greater effect on the rate of reaction than can be explained by its effect on collision rates. This resulted in the development of the Arrhenius equation which proposes a quantitative model to explain the effect of temperature change on reaction rate.

Understandings

Essential idea: The activation energy of a reaction can be determined from the effect of temperature on reaction rate.

The Arrhenius equation uses the temperature dependence of the rate constant to determine the activation energy.

A graph of 1/T against ln k is a linear plot with gradient - Ea/R and intercept, lnA.

The frequency factor (or pre-exponential factor) (A) takes into account the frequency of collisions with proper orientations.

Applications and skills

Analysing graphical representation of the Arrhenius equation in its linear form.

Describing the relationships between temperature and rate constant; frequency factor and complexity of molecules colliding.

Determining and evaluating values of activation energy and frequency factors from data.

In Chapter 6.4