Chapter 15: Problem 77
Data for the reaction $$\begin{aligned}\left[\mathrm{Mn}(\mathrm{CO})_{5}\left(\mathrm{CH}_{3}\mathrm{CN}\right)\right]^{+}+\mathrm{NC}_{5}\mathrm{H}_{5} \longrightarrow & \\\&\left[\mathrm{Mn}(\mathrm{CO})_{5}\left(\mathrm{NC}_{5}\mathrm{H}_{5}\right)\right]^{+}+\mathrm{CH}_{3} \mathrm{CN}\end{aligned}$$ are given in the table. Calculate \(E_{\mathrm{a}}\) from a plot of \(\ln k\) versus \(1 / T\) $$\begin{array}{ll}\hline T(\mathrm{K}) & k\left(\min ^{-1}\right) \\\\\hline 298 & 0.0409 \\\308 & 0.0818 \\\318 & 0.157 \\\\\hline\end{array}$$
Short Answer
Step by step solution
Understand the Arrhenius Equation
Transform the Arrhenius Equation
Organize Data for Plotting
Calculate Logarithms and Rates
Plot \( \ln k \) vs \( \frac{1}{T} \) and Determine Slope
Calculate Activation Energy \( E_a \)
Conclusion: Activation Energy Calculation
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Arrhenius Equation
To make it more practical, the Arrhenius Equation is often transformed into a linear form \( \ln k = \ln A - \frac{E_a}{R} \cdot \frac{1}{T} \). This linear form makes it easier to employ statistical tools like linear regression to analyze kinetic data. This transformation can be likened to rearranging a mathematical problem into a simpler, more approachable form, creating a straight line representation when graphed.
Kinetics
- Increased temperature typically raises reaction rates as it provides more energy to the reactants, facilitating more frequent successful collisions.
- Higher concentrations of reactants often increase reaction rates due to more particles being available to collide.
- Catalysts can speed up reactions by lowering the energy required to reach the transition state, without being consumed in the process.
Chemical Reaction Rate
- Temperature: Generally, an increase in temperature speeds up reaction rates as the molecules have more kinetic energy.
- Concentration: Higher concentrations mean more particles present to collide and react.
- Surface Area: With more surface area available, more reactant particles are directly exposed to each other, increasing collision opportunities.
- Pressure: Especially relevant for gases, where increased pressure effectively increases concentration.
Linear Regression in Chemistry
The slope of this line, which equates to \( -\frac{E_a}{R} \), provides the necessary information to find \( E_a \). Thus, the linear regression technique converts complex, nonlinear problems into simple linear problems, making computations more straightforward and accurate.
- Helps identify trends and correlations in experimental data.
- Offers a method to predict values and assess the reliability of models quantitatively.