Question

The rate of reaction between two reactants A and B decreases by a factor of 4, if the concentration of reactant B is doubled. The order of this reaction with respect to reactant B is [CBSE AIPMT 2005]

• A. - 1
• B. - 2
• C. 1
• D. 2

Answer 1

The correct option is B - 2

$A+B\to Product$
Rate, $r\propto \left[A{]}^x\right[B{]}^y\dots \dots \left(i\right)$
The rate decreases by a factor 4 if the concentration of reactant B is doubled
$\frac{1}{4}\propto \left[A{]}^x\right[2B{]}^y\dots \dots \left(ii\right)$
From Eqs. (i) and (ii)
$4={\left(\frac{1}{2}\right)}^y$
y = -2
Hence, order of reaction with respect to B is -2