Question

The rate for the reaction $2A + B \rightarrow \text{product}$ is $6 \times 10^{-4}\,\mathrm{mol\,dm^{-3}\,s^{-1}}$. Calculate the rate constant if the reaction is first order in $A$ and zeroth order in $B$. Given $[A] = [B] = 0.3\,\text{M}$

• A. $1\times10^{-3}\,\mathrm{s^{-1}}$
• B. $2\times10^{-3}\,\mathrm{s^{-1}}$
• C. $3\times10^{-3}\,\mathrm{s^{-1}}$
• D. $4\times10^{-3}\,\mathrm{s^{-1}}$

Hint:

Chemistry Tip: Zeroth order means concentration of that reactant does not affect rate.

Answer 1

The Correct Option is B

Step 1: Rate law: $$ \text{Rate}=k[A]^1[B]^0=k[A] $$

Step 2: Given rate $=6\times10^{-4}$ and $[A]=0.3$ $$ 6\times10^{-4}=k(0.3) $$

Step 3: Solve for $k$: $$ k=\frac{6\times10^{-4}}{0.3} $$

Step 4: Calculate: $$ k=2\times10^{-3}\,\mathrm{s^{-1}} $$ $$ \therefore \text{Correct option is (B).} $$