Reaction Rates 2

All chemical reactions have their “own” internal energy which is called Chemical Potential Energy (PE). Obviously, as chemical react, these energy values must change.
(Don’t you get tired and “lose” energy after doing some work?)

Consider a reaction equation:
A + B → C
Let us say that the total energy of the reactants A and B is 45kJ. (This is you before you do some work).

And after they react, they become a new product called C that now has an energy value of 25kJ. This is you after you did some work.
You have lost energy (-20kJ). The minus reminds you that you have LOST the energy.

In chemical reactions, this difference in energy between reactants and products is called “Heat of Reaction”. (ΔH = -20kJ)

In chemistry there is a natural barrier preventing chemicals from reacting. This barrier is called the Activation Energy.
For our example, let us assume that the barrier (Activation Energy) is 65kJ.
We can draw a graph showing all these energy values.

Study the graph carefully.

• 45kJ = Initial Potential Energy of Reactants
• 55kJ = Activation Energy (Energy needed to overcome barrier)
• 100kJ = Energy of the Activated Complex (In between state, neither reactants nor products)
• 25kJ = Final Potential Energy of Products
• -20kJ = Heat of Reaction (Change in the Reactants Energy Value)

By using CATALYSTS, the energy barrier (Activation Energy) can be decreased, thus allowing the reaction to run faster.

Copyright ©
V. Gokal
academic@afrihost.co.za