For an elementary reaction, $\text{2A}+\text{B}\to \text{C}+\text{D}$ , the active mass of B is kept constant but that of A is tripled. The rate of reaction will

For an elementary reaction,

$2A+B\to C+D$

Given values are;

The active mass of B is constant and concentaration of A is tripled

Rate equation expression,

$-\frac{1}{2}\frac{d\left[A\right]}{dt}=\frac{d\left[B\right]}{dt}=\frac{d\left[C\right]}{dt}=\frac{d\left[D\right]}{dt}$

Rate of reaction,

$r=K{\left[A\right]}^2{\left[B\right]}^1$

Where, r= Rate of reaction

K = rate constant

[A] = Concentration of A

[B] = Concentration of B

$r_1=K{\left[A\right]}^2{\left[B\right]}^1$ $\text{but}\text{B}\text{is}\text{constant}$ ……………(i)

$r_2=K{\left[3A\right]}^2\left[B\right]$ …….(ii)

Divide the equation (i) by equation (ii);

$\frac{r_1}{r_2}=\frac{K{\left[A\right]}^2{\left[B\right]}^1}{K{\left[3\right]}^2{\left[A\right]}^2{\left[B\right]}^1}$

$\frac{r_1}{r_2}=\frac{1}{9}$

$\therefore r_2=9r_1$