Key concepts:

• Molecules can only react with one another when they bump into one another.
• Normally, the molecules bump and bounce off; nothing happens, no chemical reaction takes place.
• If energy is added the molecules move faster, and there is more violence in their collisions.
• When the molecules collide with more violence, they break apart and their atoms re-arrange themselves into new configurations. Product molecules are formed.
• The extra energy that must be added to the moving molecules to get them to move fast enough to react with one another is the extra Activation Energy.