Questions: Determining the rate-law expression for the reaction below at the temperature at which the tabulated initial rate data were obtained: rate =
A + 2B + 3C → Products
Experiment Initial [A] Initial [B] Initial [C] Initial Rate
1 0.10 M 0.30 M 0.30 M 0.040 M/min
2 0.20 M 0.30 M 0.30 M 0.080 M/min
3 0.20 M 0.20 M 0.30 M 0.053 M/min
4 0.20 M 0.20 M 0.40 M 0.11 M/min
Transcript text: Determining the rate-law expression for the reaction below at the temperature at which the tabulated initial rate data were obtained: rate =
A + 2B + 3C → Products
Experiment | Initial [A] | Initial [B] | Initial [C] | Initial Rate
1 | 0.10 M | 0.30 M | 0.30 M | 0.040 M/min
2 | 0.20 M | 0.30 M | 0.30 M | 0.080 M/min
3 | 0.20 M | 0.20 M | 0.30 M | 0.053 M/min
4 | 0.20 M | 0.20 M | 0.40 M | 0.11 M/min
Solution
Solution Steps
Step 1: Determine the Order with Respect to A
To find the order of the reaction with respect to \( \text{[A]} \), compare experiments 1 and 2, where the concentration of \( \text{[B]} \) and \( \text{[C]} \) are constant.
The rate doubles when \([\text{A}]\) doubles, indicating a first-order reaction with respect to \( \text{[A]} \).
Step 2: Determine the Order with Respect to B
To find the order of the reaction with respect to \( \text{[B]} \), compare experiments 2 and 3, where the concentration of \( \text{[A]} \) and \( \text{[C]} \) are constant.
The rate decreases by a factor of \(\frac{0.053}{0.080} \approx 0.6625\) when \([\text{B}]\) decreases by a factor of \(\frac{0.20}{0.30} = \frac{2}{3}\). This suggests a first-order reaction with respect to \( \text{[B]} \).
Step 3: Determine the Order with Respect to C
To find the order of the reaction with respect to \( \text{[C]} \), compare experiments 3 and 4, where the concentration of \( \text{[A]} \) and \( \text{[B]} \) are constant.
The rate increases by a factor of \(\frac{0.11}{0.053} \approx 2.0755\) when \([\text{C}]\) increases by a factor of \(\frac{0.40}{0.30} = \frac{4}{3}\). This suggests a second-order reaction with respect to \( \text{[C]} \).
Final Answer
The rate-law expression for the reaction is:
\[
\boxed{\text{Rate} = k [\text{A}]^1 [\text{B}]^1 [\text{C}]^2}
\]