Math Problem Statement

The reaction C4H8(g) → 2C2H4(g) has an activation energy of 262 kJ/mol. At 600.0 K, the rate constant, k, is 6.1 × 10⁻⁸ s⁻¹. What is the value of the rate constant at 770.0 K?

Solution

To solve this problem, we need to use the Arrhenius equation in its logarithmic form to compare the rate constants at two different temperatures. The equation is given as:

ln(k2k1)=EaR(1T11T2)\ln\left(\frac{k_2}{k_1}\right) = \frac{E_a}{R} \left( \frac{1}{T_1} - \frac{1}{T_2} \right)

Where:

  • k1k_1 is the rate constant at temperature T1=600.0KT_1 = 600.0 \, \text{K},
  • k2k_2 is the rate constant at temperature T2=770.0KT_2 = 770.0 \, \text{K},
  • EaE_a is the activation energy, 262kJ/mol=262×103J/mol262 \, \text{kJ/mol} = 262 \times 10^3 \, \text{J/mol},
  • RR is the gas constant, 8.314J/mol\cdotpK8.314 \, \text{J/mol·K}.

Given:

  • k1=6.1×108s1k_1 = 6.1 \times 10^{-8} \, \text{s}^{-1},
  • T1=600.0KT_1 = 600.0 \, \text{K},
  • T2=770.0KT_2 = 770.0 \, \text{K},
  • Ea=262×103J/molE_a = 262 \times 10^3 \, \text{J/mol}.

Step-by-step solution:

  1. Calculate the difference in reciprocal temperatures: 1T11T2=1600.01770.0=0.00166670.0012987=0.000368K1\frac{1}{T_1} - \frac{1}{T_2} = \frac{1}{600.0} - \frac{1}{770.0} = 0.0016667 - 0.0012987 = 0.000368 \, \text{K}^{-1}

  2. Multiply by the activation energy and divide by the gas constant RR: EaR=262×1038.314=31,515.77K\frac{E_a}{R} = \frac{262 \times 10^3}{8.314} = 31,515.77 \, \text{K} EaR(1T11T2)=31,515.77×0.000368=11.59\frac{E_a}{R} \left( \frac{1}{T_1} - \frac{1}{T_2} \right) = 31,515.77 \times 0.000368 = 11.59

  3. Now, calculate the logarithm of the ratio of rate constants: ln(k2k1)=11.59\ln\left(\frac{k_2}{k_1}\right) = 11.59 k2k1=e11.59=107,742\frac{k_2}{k_1} = e^{11.59} = 107,742

  4. Solve for k2k_2: k2=k1×107,742=(6.1×108)×107,742=6.57×103s1k_2 = k_1 \times 107,742 = (6.1 \times 10^{-8}) \times 107,742 = 6.57 \times 10^{-3} \, \text{s}^{-1}

Thus, the rate constant at 770.0K770.0 \, \text{K} is approximately: k2=6.57×103s1k_2 = 6.57 \times 10^{-3} \, \text{s}^{-1}

Would you like more details on any step, or have any questions?

Here are 5 related questions to expand your knowledge:

  1. How does the Arrhenius equation explain the effect of temperature on reaction rates?
  2. What is the significance of activation energy in a chemical reaction?
  3. Can you derive the Arrhenius equation from first principles of chemical kinetics?
  4. How would the rate constant change if the temperature were increased to 1000 K?
  5. What happens to the rate of a reaction if the activation energy is very low?

Tip: In problems involving energy, always check unit conversions carefully—especially for activation energy.

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Math Problem Analysis

Mathematical Concepts

Chemistry
Arrhenius Equation
Exponential Functions

Formulas

Arrhenius equation: ln(k2/k1) = (Ea/R) * (1/T1 - 1/T2)
k2 = k1 * e^(Ea/R * (1/T1 - 1/T2))

Theorems

Arrhenius equation

Suitable Grade Level

Undergraduate Chemistry/Physics