Question

For a given reaction $A \rightarrow nB$, a graph is given between concentration and time. Find value of n for above reaction, based on the information given in graph for $10 \text{ min}$.

• A. 3
• B. 2
• C. 1
• D. 4

Hint:

The stoichiometric coefficient $n$ for a product B in reaction $A \rightarrow nB$ is simply the ratio of the change in concentration of B to the change in concentration of A over the same time interval.

Answer 1

The Correct Option is A

Reaction: $A \rightarrow nB$.
Time interval: $10 \text{ min}$.
Change in $[A]$: $\Delta [A] = 0.4 \text{ M} - 0.5 \text{ M} = -0.1 \text{ M}$. (Amount reacted is $0.1 \text{ M}$).
Change in $[B]$: $\Delta [B] = 0.3 \text{ M} - 0 \text{ M} = 0.3 \text{ M}$.
By stoichiometry, the ratio of rates of change must satisfy:
$-\frac{1}{1}\frac{\Delta [A]}{\Delta t} = \frac{1}{n}\frac{\Delta [B]}{\Delta t}$.
$n = - \frac{\Delta [B]}{\Delta [A]}$. (Using magnitudes of change: $n = \frac{\text{Amount B formed}}{\text{Amount A reacted}}$).
$n = \frac{0.3}{0.1}$.
$n = 3$.