Question:
For a first order reaction, the concentration changes from 0.8 to 0.4 in 15 min. The time taken for the concentration to change from 0.1 M to 0.025 M is ________.
For a first order reaction, the concentration changes from 0.8 to 0.4 in 15 min. The time taken for the concentration to change from 0.1 M to 0.025 M is ________.
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For a first order reaction, the concentration changes from 0.8 to 0.4 in 15 min. The time taken for the concentration to change from 0.1 M to 0.025 M is ____.
Updated On: Apr 15, 2026
- 30 min
- 15 min
- 7.5 min
- 60 min
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The Correct Option is A
Solution and Explanation
Step 1: Identify Half-life
The concentration drops from 0.8 to 0.4 (half) in 15 minutes. Thus, the half-life ($t_{1/2}$) is 15 minutes.
Step 2: Analyze Second Change
Concentration change: $0.1 \text{ M} \rightarrow 0.05 \text{ M} \rightarrow 0.025 \text{ M}$. This represents exactly two half-lives.
Step 3: Calculation
Total time $= 2 \times t_{1/2} = 2 \times 15 = 30 \text{ minutes}$.
Final Answer: (A)
The concentration drops from 0.8 to 0.4 (half) in 15 minutes. Thus, the half-life ($t_{1/2}$) is 15 minutes.
Step 2: Analyze Second Change
Concentration change: $0.1 \text{ M} \rightarrow 0.05 \text{ M} \rightarrow 0.025 \text{ M}$. This represents exactly two half-lives.
Step 3: Calculation
Total time $= 2 \times t_{1/2} = 2 \times 15 = 30 \text{ minutes}$.
Final Answer: (A)
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