Question

What is the concentration (in mol L\(^{-1}\)) of the product after 20 s in the following reaction:
\[ \text{A} \rightarrow 3 \text{B}, \quad \text{rate} = k[\text{A}]^0 \]

• A. 6.6 × 10\(^{-2}\)
• B. 1.32 × 10\(^{-1}\)
• C. 1.98 × 10\(^{-1}\)
• D. 2.2 × 10\(^{-2}\)

Hint:

For zero-order reactions, use \([A] = [A]_0 - k t\) and account for stoichiometry when calculating product concentration.

Answer 1

The Correct Option is C

Step 1: Find the zero-order rate constant.
For zero order: \([A]_t = [A]_0 - kt\). From the data: \(k = \frac{0.1 - 0.05}{15} \approx 3.33 \times 10^{-3}\) M/s.

Step 2: Find [B] at t = 20 s.
A consumed \(= k \times 20 = 0.0667\) M. Since A \(\to\) 3B: \([B] = 3 \times 0.0667 \approx 0.200\) M \(\approx 1.98 \times 10^{-1}\) M.
\[ \boxed{1.98 \times 10^{-1}\text{ M}} \]