Chapter 14: Problem 63
The rate constant (k) for a reaction is measured as a function of temperature. A plot of ln k versus 1>T (in K) is linear and has a slope of -7445 K. Calculate the activation energy for the reaction.
Short Answer
Expert verified
The activation energy for the reaction is 61.89243 kJ/mol.
Step by step solution
01
Understanding Arrhenius Equation
The Arrhenius Equation, which relates the rate constant, k, to the temperature, T, is given as k = A * e^{-Ea/(RT)}, where Ea is the activation energy, R is the gas constant (8.314 J/(mol*K)), and A is the pre-exponential factor. Taking the natural logarithm of both sides gives ln(k) = ln(A) - Ea/(RT). The plot of ln(k) vs. 1/T is linear with the slope equal to -Ea/R.
02
Identify the Slope
From the linear plot of ln(k) vs. 1/T, the given slope is -7445 K. This value represents the -Ea/R term in the transformed Arrhenius Equation.
03
Calculate the Activation Energy
Since the slope = -Ea/R, we can solve for Ea: Ea = -slope * R. Substituting the known values gives Ea = -(-7445 K) * (8.314 J/(mol*K)).
04
Perform the Calculation
Multiplying these values yields the activation energy: Ea = 7445 K * 8.314 J/(mol*K) = 61892.43 J/mol. Convert the energy to kilojoules by dividing by 1000: Ea = 61.89243 kJ/mol.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Activation Energy
Activation energy (\( E_a \)) is a critical concept in understanding chemical reactions. It refers to the minimum amount of energy that reacting particles must possess for a reaction to occur. This threshold energy is essential because only those particles with sufficient energy to overcome this barrier can effectively participate in a reaction, leading to product formation.
In the context of the Arrhenius Equation, the activation energy determines how sensitive a reaction rate is to temperature changes. The higher the activation energy, the more energy is required for the reaction to proceed, and the more significant the effect temperature will have on the reaction rate.
Understanding activation energy is crucial not just for predicting how a reaction will behave with temperature variations, but also for catalysis, as catalysts work by lowering the activation energy, therefore increasing the reaction rate without the need for increasing temperature.
In the context of the Arrhenius Equation, the activation energy determines how sensitive a reaction rate is to temperature changes. The higher the activation energy, the more energy is required for the reaction to proceed, and the more significant the effect temperature will have on the reaction rate.
Understanding activation energy is crucial not just for predicting how a reaction will behave with temperature variations, but also for catalysis, as catalysts work by lowering the activation energy, therefore increasing the reaction rate without the need for increasing temperature.
Rate Constant
The rate constant (\( k \) represents the proportionality factor that connects the rate of a chemical reaction to the concentrations of the reactants. It is a measure of the speed at which a reaction proceeds and is heavily influenced by factors such as activation energy and reaction temperature.
In the Arrhenius Equation, the rate constant links directly to the temperature and activation energy, providing a mathematical expression of how these variables affect the reaction rate. The equation shows an exponential relationship between the rate constant and the inverse of the temperature (\( \frac{1}{T} \) meaning that even slight changes in temperature can lead to significant differences in the rate constant.
This behaviour explains why controlling temperature is crucial in industrial chemical processes and why understanding how to calculate and interpret the rate constant is vital for chemists and engineers.
In the Arrhenius Equation, the rate constant links directly to the temperature and activation energy, providing a mathematical expression of how these variables affect the reaction rate. The equation shows an exponential relationship between the rate constant and the inverse of the temperature (\( \frac{1}{T} \) meaning that even slight changes in temperature can lead to significant differences in the rate constant.
This behaviour explains why controlling temperature is crucial in industrial chemical processes and why understanding how to calculate and interpret the rate constant is vital for chemists and engineers.
Reaction Temperature
Reaction temperature is a critical factor in determining the rate at which chemical reactions occur. The Arrhenius Equation highlights the impact that temperature has on the rate constant and, by extension, on the reaction speed. As temperature increases, particles move faster, leading to more frequent and more energetic collisions, thus increasing the probability of surpassing the activation energy barrier.
A practical measure of this relationship is seen in the activation energy's influence on the rate constant for different temperatures. The negative relationship indicated by the Arrhenius Equation (\( \text{ln}(k) = \text{ln}(A) - \frac{E_a}{RT} \) suggests that an increase in temperature will exponentially increase the rate constant, hence accelerating the reaction rate. On the other hand, a decrease in temperature can dramatically slow down a reaction.
Analysts often analyze temperature's effect on reaction rates by plotting the natural logarithm of the rate constant against the reciprocal of the temperature, as seen in the exercise. This graphical representation can provide valuable insights into not only the activation energy but also the overall kinetics of the reaction.
A practical measure of this relationship is seen in the activation energy's influence on the rate constant for different temperatures. The negative relationship indicated by the Arrhenius Equation (\( \text{ln}(k) = \text{ln}(A) - \frac{E_a}{RT} \) suggests that an increase in temperature will exponentially increase the rate constant, hence accelerating the reaction rate. On the other hand, a decrease in temperature can dramatically slow down a reaction.
Analysts often analyze temperature's effect on reaction rates by plotting the natural logarithm of the rate constant against the reciprocal of the temperature, as seen in the exercise. This graphical representation can provide valuable insights into not only the activation energy but also the overall kinetics of the reaction.