ACTIVATION ENERGY
Temperature and Rate of Reactions
For a chemical reaction to occur, molecules must undergo effective collisions with the
necessary energy (called the activation energy) for the reaction to take place.
Temperature and Rate of Reactions
■ The following energy diagrams show an exothermic and an endothermic reaction.
■ The “energy hill” represent the activation energy (Ea).
■ The higher the activation energy, the slower the reaction, conversely, the lower the
activation energy, the faster the reaction.
■ At the top of the “energy hill” is the transition state where bond breaking and bond
forming is taking place.
Temperature and Reaction Rate
■ Several factor affect the energy of activation. However, in this section will focus on how
temperature affects the energy of activation, which in turn affects the rate of the
reaction.
■ The Maxwell-Boltzman distribution curve shows the effect of temperature on the kinetic
energy of molecules.
■ When the temperature increases, the average speed of molecules increases and the
number of molecules with KE greater than Ea also increase. This means that there will
be an increase in the number of effective collision. It is the increase in the number of
effective collisions that is mainly responsible for the increase in the reaction rate as the
temperature is increased.
Arrhenius Equation
Using the Arrhenius equation to calculate the activation
energy
■ If we take the natural logarithm of both sides of the Arrhenius equation, we find that: