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Ch.14 - Chemical Kinetics
Chapter 14, Problem 137a

Values of Ea = 6.3 kJ/mol and A = 6.0⨉108/(M s) have been measured for the bimolecular reaction: NO(g) + F2(g) → NOF(g) + F(g) (a) Calculate the rate constant at 25 °C.

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Convert the temperature from Celsius to Kelvin by adding 273.15 to the given temperature in Celsius: \( T = 25 + 273.15 \).
Use the Arrhenius equation to relate the rate constant \( k \) to the activation energy \( E_a \), the frequency factor \( A \), and the temperature \( T \): \( k = A \cdot e^{-E_a/(RT)} \).
Substitute the given values into the Arrhenius equation: \( A = 6.0 \times 10^8 \text{ M}^{-1}\text{s}^{-1} \), \( E_a = 6.3 \text{ kJ/mol} \) (convert to J/mol by multiplying by 1000), and \( R = 8.314 \text{ J/mol K} \).
Calculate the exponent in the Arrhenius equation: \( -E_a/(RT) \).
Substitute the calculated exponent back into the Arrhenius equation to find the rate constant \( k \).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Arrhenius Equation

The Arrhenius equation relates the rate constant of a reaction to the temperature and activation energy. It is expressed as k = A * e^(-Ea/RT), where k is the rate constant, A is the pre-exponential factor, Ea is the activation energy, R is the universal gas constant, and T is the temperature in Kelvin. This equation helps predict how changes in temperature affect reaction rates.
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Activation Energy (Ea)

Activation energy is the minimum energy required for a chemical reaction to occur. It represents the energy barrier that reactants must overcome to form products. In the context of the Arrhenius equation, a lower Ea results in a higher rate constant, indicating that the reaction can proceed more quickly at a given temperature.
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Rate Constant (k)

The rate constant is a proportionality factor in the rate law of a chemical reaction, indicating the speed of the reaction. It varies with temperature and is influenced by factors such as activation energy and molecular collisions. For bimolecular reactions, the rate constant can be calculated using the Arrhenius equation, which incorporates temperature and activation energy.
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Related Practice
Open Question
The reaction AS C is first order in the reactant A and is known to go to completion. The product C is colored and absorbs light strongly at 550 nm, while the reactant and intermediates are colorless. A solution of A was prepared, and the absorbance of C at 550 nm was measured as a function of time. (Note that the absorbance of C is directly proportional to its concentration.) Use the following data to determine the half-life of the reaction.
Textbook Question

Values of Ea = 6.3 kJ/mol and A = 6.0⨉108/(M s) have been measured for the bimolecular reaction: NO(g) + F2(g) → NOF(g) + F(g) (d) Why does the reaction have such a low activation energy?

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Textbook Question
A 1.50 L sample of gaseous HI having a density of 0.0101 g>cm3 is heated at 410 °C. As time passes, the HI decomposes to gaseous H2 and I2. The rate law is -Δ3HI4>Δt = k3HI42, where k = 0.031>1M ~ min2 at 410 °C. (b) What is the partial pressure of H2 after a reaction time of 8.00 h?
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Textbook Question
The rate constant for the decomposition of gaseous NO2 to NO and O2 is 4.7>1M ~ s2 at 383 °C. Consider the decomposition of a sample of pure NO2 having an initial pressure of 746 mm Hg in a 5.00 L reaction vessel at 383 °C. (c) What is the mass of O2 in the vessel after a reaction time of 1.00 min?
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