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15240672380's Question
Chemistry
Posted 5 months ago

2)

An experimental investigation into the kinetics of a first order liquid phase reaction gave the following results:
\begin{tabular}{ccc}
\begin{tabular}{c} 
Reactant \\
Concentration \\
(kmol m3)\left(\mathbf{k m o l ~ m}^{-\mathbf{3}}\right)
\end{tabular} & \begin{tabular}{c} 
Rate of reaction \\
(kmol m3s1)\left(\mathbf{k m o l ~ m}^{-3} \mathbf{s}^{-1}\right)
\end{tabular} & \begin{tabular}{c} 
Temperature \\
(C)\left({ }^{\circ} \mathbf{C}\right)
\end{tabular} \\
3.96 & 6.85×1036.85 \times 10-3 & \\
3.20 & 8.10×1038.10 \times 10-3 & 20.0 \\
2.94 & 11.55×10311.55 \times 10-3 & 25.7 \\
1.82 & 12.01×10312.01 \times 10-3 & 32.8 \\
0.43 & 4.37×1034.37 \times 10-3 & 41.8 \\
& & 49.8
\end{tabular}

Show that the variation of rate constant with temperature is represented by the Arrhenius equation and evaluate the activation energy of reaction and the pre-exponential factor.
[46.04 kJ mol1 and 28.21×104 s1]
\left[46.04 \mathrm{~kJ} \mathrm{~mol}^{-1} \text { and } 28.21 \times 10^{4} \mathrm{~s}^{-1}\right]
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Answer from Sia
Posted 5 months ago
Solution
1
Understand the Arrhenius equation: The Arrhenius equation relates the rate constant kk of a reaction to the temperature TT (in Kelvin), the activation energy EaE_a, and the pre-exponential factor AA. It is given by k=AeEaRTk = A e^{-\frac{E_a}{RT}}, where RR is the gas constant (8.314 J mol1^{-1} K1^{-1})
2
Linear form of the Arrhenius equation: To evaluate the activation energy and the pre-exponential factor, we use the linear form of the Arrhenius equation: ln(k)=ln(A)EaRT\ln(k) = \ln(A) - \frac{E_a}{RT}. A plot of ln(k)\ln(k) versus 1T\frac{1}{T} should yield a straight line with a slope of EaR-\frac{E_a}{R} and an intercept of ln(A)\ln(A)
3
Convert temperatures to Kelvin and calculate $\ln(k)$: Convert each temperature from degrees Celsius to Kelvin by adding 273.15. Then, calculate the natural logarithm of each rate constant ln(k)\ln(k)
4
Plot and determine slope and intercept: Plot ln(k)\ln(k) versus 1T\frac{1}{T} to determine the slope and intercept. The slope will give EaR-\frac{E_a}{R}, and the intercept will give ln(A)\ln(A)
5
Calculate $E_a$ and $A$: Use the slope to calculate the activation energy EaE_a by multiplying the slope by R-R. Then, exponentiate the intercept to find the pre-exponential factor AA
Answer
The activation energy EaE_a is 46.04 kJ mol1^{-1} and the pre-exponential factor AA is 28.21×10528.21 \times 10^5 s1^{-1}.
Key Concept
The Arrhenius equation relates the rate constant of a reaction to the temperature, activation energy, and pre-exponential factor.
Explanation
By plotting the natural logarithm of the rate constant against the inverse of the temperature in Kelvin, we can determine the activation energy and pre-exponential factor from the slope and intercept of the resulting line.

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