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The decomposition of H2O2 is first order. Over 50 minutes its concentration drops from 0.5 M to 0.125 M. When the concentration of H2O2 reaches 0.05 M, what is the rate of formation of O2? (Reaction: 2H2O2 -> 2H2O + O2)
- 1.34 * 10⁻² mol min⁻¹
- 6.93 * 10⁻² mol min⁻¹
- 6.93 * 10⁻⁴ mol L⁻¹ min⁻¹
- 2.66 L min⁻¹ at STP
Correct answer: 6.93 * 10⁻⁴ mol L⁻¹ min⁻¹
Solution
0.5 to 0.125 M is two half-lives in 50 min, so t1/2 = 25 min and k = 0.693/25 = 0.0277 min⁻¹; rate of O2 = (1/2)k[H2O2] = (1/2)(0.0277)(0.05) = 6.93*10⁻⁴ mol L⁻¹ min⁻¹.
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