Define the following:
(i) Elementary step in a reaction
(ii) Rate of a reaction
(i) Elementary step in a reaction: Those reactions which take place in one step are called elementary reactions. Example: Reaction between H2 and I2 to form 2HI
H2 + I2 2HI
(ii) Rate of a reaction: The change in the concentration of any one of the reactants or products per unit time is called rate of reaction.