Write two factors affecting the rate of chemical reaction.

Hint: Chemical reactions occur when two reactant molecules collide effectively, each having minimum energy and proper orientation. Reactant concentration, physical state of the reactants, surface area, temperature and the presence of a catalyst are some factors that affect reaction rate.

Complete step by step answer:
-The rate of reaction refers to the speed at which the products are formed from the reactants in a chemical reaction. It gives some insight into the time frame under which a reaction can be completed. Reaction kinetics is the study of the rate of chemical reactions, and reaction rates can vary greatly over a large range of time scales. The two main factors that affect the rate of a chemical reaction are the nature of reactants and surface area.
-According to the collision theory, increasing the concentration of one or more reactants increases the rate of reaction because a higher concentration of a reactant leads to more collisions of that reactant in a specific time scale. The physical state of reactants, number of reactants and complexity of reaction affects in such a way that the rate of reaction is generally slower in liquids when compared to gases and slower in solids when compared to liquids. So, the size of the reactant also affects. Smaller the size of the reactant, faster is the reaction.
-Since reactant molecules exist in different phases in a heterogeneous mixture, the rate of reaction is limited by the contact surface area of the phases. The surface area of reactants affects the rate of reaction such that if the size of a particle is small, the surface area will be more and this increases the speed of heterogeneous chemical reactions.
Few more important factors are: 1) An increase in temperature increases the rate of reaction due to rise in the average kinetic energy of the reactant molecules. Thus, a greater proportion of molecules will have the minimum energy that is necessary for an effective collision.
2) A catalyst is a substance that accelerates a reaction by participating in it without being consumed and increases the rate of the reaction without actually participating in the reaction. It increases the speed of reaction in both forward and reverse reaction by following an alternate pathway which has lower activation energy.

Note:
Pressure also affects the rate of chemical reaction. Pressure increases the concentration of gases which results in the increase of the rate of reaction in the direction of less gaseous molecules and decreases in the reverse direction.