Question

Consider the reaction, $2A+B⟶$ Products. When the 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 the rate constant for this reaction is:

• A. $s^{-1}$
• B. $L$ ${mol}^{-1}{s}^{-1}$
• C. Unitless
• D. $mol$ $L^{-1}{s}^{-1}$

Answer 1

Answer: (B)

$L$ ${mol}^{-1}{s}^{-1}$

Concentration change in '$B$' does not change half life, it means the reaction is first order with respect to $B$. When concentration of only '$A$' is doubled, the rate of reaction becomes double, thus order with respect to $A$ will also be one.
Overall order of reaction $=2$
Unit of rate constant $=L$ ${mol}^{-1}{s}^{-1}$