Potential Energy Diagrams

Drill – 5/22/08 1. What is the general rate law format? 2. For the following rate law R = k[H2]2[O2] If the concentration of H2 is tripled, what happens to the rate? If the concentration of O2 is tripled, what happens to the rate?

Will two molecules that never encounter each other react? NO! In order for molecules to react they must collide. Collision Theory states that in order for two atoms, ions, or molecules can react to form products when the collide IF they have enough energy.

This energy is called the ACTIVATION ENERGY This energy is called the ACTIVATION ENERGY. It is the minimum energy that colliding particles must have in order to react.

Let’s consider the reaction between hydrogen and oxygen to form water: 2H2 + O2  2H2O + 

Activated Complex - An unstable arrangement of atoms forms momentarily at the activation-energy barrier. Also called TRANSITION STATE. Reactants Energy  Products Time 

Endothermic or Exothermic??? Activated Complex Activation Energy Reactants Energy  Heat of Reaction (ΔH) Products Time 

Now let’s look at an endothermic reaction. What will have higher energy, the reactants or the products? Will the Heat of Reaction (ΔH) be positive or negative?

Endothermic or Exothermic??? Activated Complex Activation Energy Products Energy  Heat of Reaction (ΔH) Reactants Time 

Catalyst A CATALYST increases the rate of reaction by lowering the activation-energy barrier.

Does a catalyst affect the Heat of Reaction? Activation Energy without catalyst Activation Energy with catalyst Reactants Energy  Heat of Reaction (ΔH) Products Time 

How does the catalyst affect the magnitude of the activation energy? Does the catalyst change the amount of energy released in the reaction? Along which of the two reaction paths are reactants converted more rapidly to products?