A reaction occurs each time particles of the reactants collide.
- each time particles of the reactants collide couldn't be everytime also a sucess reaction (form product). another factor to be consider is collision geometry, enough energy and etc.

Optimum collision geometry lowers the activation energy barrier.
- when there is the right geometry of collision, the reaction will be happened immediately without need of energy (higher temperature). this will lowers the activation energy.

The slowest reaction incolved in a reaction mechanism determines the rate of overall reaction.
- the slowest is the determines the rate because we only could calculate the rate of reaction when all the reaction is finish. meaning that there is no reactant remaining in the reaction.