Question

In a zero-order reaction,the reactant A disappeared with a rate of reaction k=0.04 Msec^-1. The initial concentration of A is 1 M. What will be the concentration of A after 20 seconds?

• A. 1.08 M
• B. 0.2 M
• C. 0.8 M
• D. 0.002 M
• E. 0.008 M

Answer 1

The Correct Option is B

Given parameters:

• Rate constant \( k = 0.04 \, \text{M sec}^{-1} \)
• Initial concentration \( [A]_0 = 1 \, \text{M} \)
• Time \( t = 20 \, \text{sec} \)
• Zero-order reaction kinetics

 

Zero-order rate equation: \[ [A]_t = [A]_0 - kt \] \[ [A]_t = 1 - (0.04 \times 20) \] \[ [A]_t = 1 - 0.8 = 0.2 \, \text{M} \]

Thus, the correct option is (B): 0.2 M.

Answer 2

1. Zero-order reaction rate law:

For a zero-order reaction, the rate of reaction is independent of the concentration of the reactant. The integrated rate law for a zero-order reaction is:

\[[A]_t = [A]_0 - kt\]

where:

• \([A]_t\) is the concentration of A at time \(t\)
• \([A]_0\) is the initial concentration of A
• \(k\) is the rate constant
• \(t\) is the time elapsed

2. Substitute the given values:

\([A]_0 = 1 \, M\)

\(k = 0.04 \, M \, sec^{-1}\)

\(t = 20 \, sec\)

\[[A]_t = 1 - (0.04)(20)\]

3. Perform the calculation:

\[[A]_t = 1 - 0.8 = 0.2 \, M\]

4. Final answer:

The concentration of A after 20 seconds is 0.2 M.

Thus, the correct option is (B) 0.2 M.