Question

Given above is the concentration vs time plot for a dissociation reaction : $A \to nB$. Based on the data of the initial phase of the reaction (initial 10 min), the value of n is ____.

• A. 4
• B. 5
• C. 2
• D. 3

Hint:

The ratio of changes in concentration $\Delta[Product] / |\Delta[Reactant]|$ gives the stoichiometric coefficient of the product (assuming reactant coefficient is 1).

Answer 1

The Correct Option is A

From the graph (Solid line A), concentration drops from 0.05 to 0.04 in 10 mins.
$-\Delta [A] = 0.01 \text{ M}$.
From the graph (Dashed line B), concentration rises from 0 to 0.04 in 10 mins.
$\Delta [B] = 0.04 \text{ M}$.
Stoichiometry: Rate $= -\frac{d[A]}{dt} = \frac{1}{n} \frac{d[B]}{dt}$.
Change ratio: $n = \frac{\Delta [B]}{-\Delta [A]} = \frac{0.04}{0.01} = 4$.