Verified Solution • 2025–26 Session moderate

QJEEM07Ch59f7: JEE Main 2007 Chemistry - Class 12 JEEM07Ch59f7 Solution: Consider the reaction, 2A + B products. When concentration of B …

Consider the reaction, 2A + B →\to products. When concentration of B alone was doubled, the half-life did not change. When the concentration of A alone was doubled, the rate increased by two times. The unit of rate constant for this reaction is

Multiple Choice Options

  • A L mol-1 s-1
  • B no unit
  • C mol L-1 s-1
  • D s-1

Step-by-Step Verified Solution

Rate = k [A]x[B]y

When [B] is doubled, keeping [A] constant half-life of the reaction does not change.

For a first order reaction t1/2=0.693K  {t_{1/2}} = {{0.693} \over K}\,\, i.e. for a first order reaction t1/2{t_{1/2}} does not depend up on the concentration. Hence the reaction is first order with respect to B. Now when [A] is doubled, keeping [B] constant, the rate also doubles. Hence the reaction is first order with respect to A.

∴\therefore      \,\,\,\,\, Rate = k [A]1[B]1

Order of reaction =1+1=2=1+1=2

Now for a nth order reaction, unit of rate constant is
(L)n–1 (mol)1–n s–1 when n = 2, unit of rate constant
is L  mol−1 sec⁡−1.L\,\,mo{l^{ - 1}}\,{\sec ^{ - 1}}.

Related Learning Resources & Exam Preparation

JEE Main PYQ Question Bank
Browse year-wise authentic previous years' questions with solutions
Authentic CBT Mock Tests
Simulate official exam environment with live timer and percentile scoring