N2O5 dissolved in chloroform decomposes by a first order path with k = 6.2 x 10^-4 per minute. What is the rate when [N2O5] = 0.40 M?
A2.5 x 10^-4 mol/L/min
B1.6 x 10^-3 mol/L/min
C6.2 x 10^-4 mol/L/min
D9.9 x 10^-5 mol/L/min
Answer & Solution
Correct answer: A. 2.5 x 10^-4 mol/L/min
1. A first order rate law reads rate = k[N2O5].
2. Substituting gives 6.2 x 10^-4 min^-1 x 0.40 mol/L.
3. The product is 2.5 x 10^-4 mol/L/min.
4. Units check: per minute times mol per litre gives mol per litre per minute.
5. The value 1.6 x 10^-3 divides k by the concentration instead of multiplying, and 9.9 x 10^-5 squares the concentration as if the reaction were second order.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 12 "Kinetics", section 12.3 Rate Laws_
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