Collision Theory 

The Basics-

In order for a reaction to take place, particles must, collide and they must collide with enough enery to react. The minimum amount of energy needed for a reaction to take place is called the activation energy. Only a small proportion of collisions have enough energy to react, which results in a small proprtion of collisions.
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The faster the particles are moving the more energy they have. The fast moving particles are more likely to collide with each other resulting in a more successful reaction. You can increase the speed of the particles by heating them up.