Multiple Choice
The reactant concentration in a first-order reaction was 7.30 × 10^(-2) M after 25.0 s and 9.50 × 10^(-3) M after 95.0 s. What is the rate constant for this reaction?
15. Chemical Kinetics
Integrated Rate Law
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For the decomposition of urea, NH2CONH2 (aq) + H+(aq) + 2 H2O (l) → 2 NH4+ (aq) + HCO3– (aq), the rate constant is 3.24 × 10–4 s–1 at 35°C. The initial concentration of urea is 2.89 mol/L. What fraction of urea has decomposed after 3.5 minutes?
A
0.934
B
0.0658
C
1.13×10–3
D
0.0235
Verified step by step guidance1
Identify the type of reaction and the order of the reaction. The decomposition of urea is a first-order reaction, as indicated by the units of the rate constant (s-1).
Use the first-order kinetics formula to relate the concentration of reactant over time: , where is the concentration at time t, is the initial concentration, k is the rate constant, and t is the time.
Convert the time from minutes to seconds to match the units of the rate constant. Since 3.5 minutes is given, convert it to seconds: .
Substitute the known values into the first-order kinetics formula: .
Calculate the fraction of urea decomposed using the formula: . This will give you the fraction of urea that has decomposed after 3.5 minutes.
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