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N2O5 decomposes by first-order kinetics into NO2 and O2. Over the first 50 minutes the total pressure in a constant-volume vessel rises from 50 mmHg to 87.5 mmHg. What will the total pressure be after 100 minutes (at constant temperature)?
- 116.25 mmHg
- 175.0 mmHg
- 106.25 mmHg
- 136.25 mmHg
Correct answer: 106.25 mmHg
Solution
If x mmHg of N2O5 reacts, total P = 50 + 1.5x; at 50 min P = 87.5 gives x = 25 (N2O5 halved), so 50 min is one half-life. After 100 min (two half-lives) N2O5 = 12.5 mmHg, giving total P = 106.25 mmHg.
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