# NEET Chemistry Chemical Kinetics Questions Solved

A gaseous substance $A{B}_{3}$ decomposes irreversibly according to the overall equation $A{B}_{3}\to \frac{1}{2}{A}_{2}+\frac{3}{2}{B}_{2}$ Starting with pure $A{B}_{3}$ the partial pressure of the reactant varies with time for which the data are given below.
Time in hours 0      5.0      15.0       53.0

${P}_{A{B}_{3}}$mm Hg  660   330      165       82.5

What is the order of the reaction ?

(A) 2

(B) 0.5

(C) 1

(D) 1.5

(A).  Examining the data from 660 mm to 330 mm, ${T}_{1/2}$ = 5 hrs then from 330 mm to 165 mm, ${T}_{1/2}$ = (15.0 – 5.0)hrs = 10 hrs From 165 mm to 82.5 mm, ${T}_{1/2}$ = (35 – 15)hrs = 20 hrs Thus ${T}_{1/2}$ values are inversely proportional to partial pressure of the reactant. Since no complication such as backward reaction or auto catalysis is envisaged each of the pressure values, 660 mm, 330 mm, .... may be regarded as initial concentration for the next ${T}_{1/2}$ period.

Hence order=2

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