What effect does the concentration of reactants have on the rate of a reaction apex?

Concentration of reactant mostly accelerates the rate of a reaction(at a higher concentration, reactants collide more often).

Explanation:

When there is more concentration of reactants then it means there are more number of molecules. Hence, then there will be more number of collisions taking place in the chemical reaction.

As a result, rate of reaction will increase with increase in concentration.

On the other hand, when there is decrease in concentration of reactants then it means less number of reactant molecules are taking part in the chemical reaction.

Hence, there will be less number of collisions between the molecules due to which there will be decrease in the rate of reaction.