Question

Ford elementary reaction M ------> N (M gives N), the rate of disappearance of M is increased by factor of 8 upon doubling the concentration of M. the order of the reaction with respect to M is:

A) 4

B)3

C)2

D)1

[ Doubt: what does order of reaction mean. ]

Answer 1

The order of a reaction is a numerical value (1st, 2nd, 3rd) that denotes how the concentration of one species changes when the amount of another species changes, in a chemical reaction. If by doubling a reactant and one observes the product concentration double, the order is said to be 1st order, with respect to the reactant. If the reactant concentration is doubled and the product concentration does not change, the order is said to be 0th order with respect to the reactant. If it is doubled and the other concentration quadruples, the order is said to be 2nd order with respect to the reactant.
Now, regarding a reaction order. If there is one reactant, then the order of the reaction is the same as the order of the reactant. If there are two reactants, and one shows 1st order and the other shows 0th order, then the reaction is the sum of the two orders, thus 1st order for this example.