Question

The molecularity of a reaction is :

• A. always two
• B. same as its order
• C. different than the order
• D. may be same or different as the order

Answer 1

Answer: (D)

The number of reacting species (atoms, ions or molecules) which must collide simultaneously in order to bring about the chemical reaction is called molecularity of reaction. It is always a natural number $(1,2,3$ etc. $)$
Order of a reaction is the sum of the powers of concentration terms in the rate law. It is determined experimentally and can have zero and fractional value also. Molecularity and order of reaction for any given reaction may be same or different.
$2HI\stackrel{\text{Air}}{\to }{H}_2+I_2$
order $=0$, molecularity $=2$
$2NO+O_2\to 2N{O}_2$,
order $=3$, molecularity $=3$