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Ch.14 - Chemical Kinetics
Chapter 14, Problem 85

The enzyme carbonic anhydrase catalyzes the reaction CO2(g) + H2O(l) ↔ HCO3⁻(aq) + H⁺(aq). In water, without the enzyme, the reaction proceeds with a rate constant of 0.039 s⁻¹ at 25 _x001E_C. In the presence of the enzyme in water, the reaction proceeds with a rate constant of 1.0 * 10⁶ s⁻¹ at 25 _x001E_C. Assuming the collision factor is the same for both situations, calculate the difference in activation energies for the uncatalyzed versus enzyme-catalyzed reaction.

Verified step by step guidance
1
Identify the Arrhenius equation: k = A * e^(-Ea/(RT)), where k is the rate constant, A is the pre-exponential factor (collision factor), Ea is the activation energy, R is the gas constant (8.314 J/(mol*K)), and T is the temperature in Kelvin.
Since the collision factor (A) is the same for both reactions, use the Arrhenius equation to set up the ratio of the rate constants: k1/k2 = e^((Ea2 - Ea1)/(RT)), where k1 and k2 are the rate constants for the uncatalyzed and catalyzed reactions, respectively.
Take the natural logarithm of both sides of the equation to solve for the difference in activation energies: ln(k1/k2) = (Ea2 - Ea1)/(RT).
Substitute the given rate constants (k1 = 0.039 s⁻¹ and k2 = 1.0 * 10⁶ s⁻¹) and the temperature (T = 25°C = 298 K) into the equation: ln(0.039 / (1.0 * 10⁶)) = (Ea2 - Ea1)/(8.314 * 298).
Solve the equation for the difference in activation energies (Ea2 - Ea1) by multiplying both sides by (8.314 * 298) to isolate (Ea2 - Ea1).

Key Concepts

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

Activation Energy

Activation energy is the minimum energy required for a chemical reaction to occur. It represents the energy barrier that reactants must overcome to transform into products. In the context of enzyme-catalyzed reactions, enzymes lower the activation energy, allowing reactions to proceed more quickly and efficiently compared to uncatalyzed reactions.
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Activity Series Chart

Rate Constant

The rate constant (k) is a proportionality factor in the rate equation of a chemical reaction, reflecting the speed of the reaction at a given temperature. It is influenced by factors such as temperature and the presence of catalysts. In this question, the significant difference in rate constants for the uncatalyzed and enzyme-catalyzed reactions indicates how much the enzyme accelerates the reaction.
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Rate Constant Units

Arrhenius Equation

The Arrhenius equation relates the rate constant of a reaction to its activation energy and temperature. It is expressed as k = A * e^(-Ea/RT), where A is the pre-exponential factor, Ea is the activation energy, R is the gas constant, and T is the temperature in Kelvin. This equation allows for the calculation of activation energies by comparing rate constants of reactions under different conditions.
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Related Practice
Textbook Question

Many metallic catalysts, particularly the precious-metal ones, are often deposited as very thin films on a substance of high surface area per unit mass, such as alumina (Al2O3) or silica (SiO2). (b) How does the surface area affect the rate of reaction?

Textbook Question

The enzyme urease catalyzes the reaction of urea, (NH2CONH2), with water to produce carbon dioxide and ammonia. In water, without the enzyme, the reaction proceeds with a first-order rate constant of 4.15 × 10-5 s-1 at 100°C. In the presence of the enzyme in water, the reaction proceeds with a rate constant of 3.4 × 104 s-1 at 21°C. (b) If the rate of the catalyzed reaction were the same at 100°C as it is at 21°C, what would be the difference in the activation energy between the catalyzed and uncatalyzed reactions?

Textbook Question

The enzyme urease catalyzes the reaction of urea, (NH2CONH2), with water to produce carbon dioxide and ammonia. In water, without the enzyme, the reaction proceeds with a first-order rate constant of 4.15 × 10-5 s-1 at 100°C. In the presence of the enzyme in water, the reaction proceeds with a rate constant of 3.4 × 104 s-1 at 21°C. (c) In actuality, what would you expect for the rate of the catalyzed reaction at 100°C as compared to that at 21°C?

Textbook Question

The activation energy of an uncatalyzed reaction is 95 kJ/mol. The addition of a catalyst lowers the activation energy to 55 kJ/mol. Assuming that the collision factor remains the same, by what factor will the catalyst increase the rate of the reaction at (a) 25 C

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