The rate at which a reaction occurs depends on three factors:
How frequently do reaction collisions occur?
What fraction of the collisions have sufficient energy for the reaction to occur (bonding breaking, bond making)?
What fraction of the reactions have the correct orientation for the reaction to occur?
Increasing the concentration of the reactants often increases
the rate of the reaction by increasing the frequency at which
collisions occur.
Contrapositive- as the reaction progresses, the concentration of reactants decreases, and the rate of reaction decreases.
Increasing the temperature often increases the rate of the reaction by increasing the fraction of collisions with sufficient energy for a reaction to occur. This will be quantified with the Arrhenius Equation.