Question

(a) What do you mean by rate of a reaction?
(b) What will be the effect of temperature on the rate of a reaction?

Answer 1

Hint: The branch of chemistry that deals with the study of the speeds or the rates of chemical reactions, the factors affecting the rates of the chemical reactions and the mechanisms by which the reaction proceeds is known as chemical kinetics.

Complete answer:
(a) The rate of a reaction is simply the speed with which the reaction takes place. The speed or rate of the reaction is expressed either in terms of decrease in the concentration of the reactant per unit time or increase in the concentration of the product per unit time. Thus, we can define rate of a reaction as;
The rate of reaction is the change in the concentration of any one of the reactants or product per unit time.
Consider a reaction; $R \to P$
$Rate = \dfrac{{ - \Delta [R]}}{{\Delta t}} = \dfrac{{\Delta [P]}}{{\Delta t}}$
The negative sign in the first term is simply to show that the concentration of reactant is decreasing while the positive sign in the second term signifies that the concentration of product is increasing.
(b) The rate of a reaction increases with increase in temperature. It was found that in most of the cases, the reaction rate becomes nearly double for ${10^o}$ rise in temperature. In some cases, the reaction doesn’t take place at room temperature but takes place at higher temperature. At higher temperatures, due to more thermal energy the particles move faster and collide frequently. As a result of which the rate of reaction increases.

Note:
 We have seen the rate of the reaction and its dependence on temperature. It should be noted that the unit of rate of reaction is $mol{L^{ - 1}}{\sec ^{ - 1}}$ . In case of gaseous reactants and products, pressure is used and the unit of rate of reaction are $atm{\min ^{ - 1}}$ or $atm{\sec ^{ - 1}}$ .