Question

For a reaction $A+B \to $ Products, it is observed the doubling the concentration of $B$ causes the reaction rat to increase four times, but doubling the concentration of $A$ has no effect on the rate of reaction. The rate equation is therefore

• A. rate $=k[A]^{2}$
• B. rate $=k[B]^{2}$
• C. rate $=k[A][B]$
• D. rate $=k[A]$

Answer 1

Answer: (B)

$A+B \rightarrow$ Products

Let $ R_{1}=k[A]^{x}[B]^{y}\,\,\,\,\, \dots(i)$

When $B^{\prime}=2 B, R_{2}=4 R_{1}$

Rate, $4 R_{1}=k[A]^{x}[2 B]^{y}\,\,\,\,\, \dots(ii)$

From equation (i) and (ii)

$4=\frac{[A]^{x}[2 B]^{y}}{[A]^{x}[B]^{y}}$

$ \Rightarrow 4=[2]^{y}$

$ \Rightarrow y=2$

As concentration of $A$ have not effect, thus $x=0$

Rate $=k[A]^{0}[B]^{2}=k[B]^{2}$