## Rate of Chemical Reaction Chemistry Notes

Rate of Chemical Reaction :

When a chemical reaction takes place the concentration of reactants decreases while the concentration of products increases. So, “the change in concentration of a reactant or product with time is called rate of reaction.”
Its unit is mol L-1 sec-1 or mol L-1 min-1

It is of two types:

• Average rate.
• Instantaneous rate.

Average Rate :

The change in concentration of reactants or products in a chemical reaction per unit time is called average rate of reaction.

→ It is clear from figure 4.1 that the concentration of reactant decreases with time while the concentration of product increases. According to law of mass action, the rate of reaction is directly proportional to the concentration of reactant so if the concentration of reactant increases then the rate of reaction also increases and if concentration of reactant decreases then rate of reaction also decreases. Hence, the rate of reaction decreases with time because the concentration of reactant also decreases.

Instantaneous Rate :

→ The actual rate of reaction at a particular moment of time is called instantaneous rate. It is different from average rate.

Instantaneous rate = $$\frac{d C}{d t}$$

→ Here, the rate of rction is represented by $$\frac{d C}{d t}$$, where minimum increase dC takes place in the concentration of product at infinitiesimally small interval of time di and minimum decrease dC takes place in the concentration of reactants.