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Chapter 13: Problem 49

What do we mean by activation energy?

Short Answer

Expert verified
Activation energy (\(E_a\)) is the minimum amount of energy required for a chemical reaction to proceed, acting as an energy barrier that must be overcome for reactants to turn into products. It plays a crucial role in determining the reaction rate, with higher activation energies leading to slower reaction rates. The relationship between temperature and activation energy is described by the Arrhenius equation, which indicates that an increase in temperature leads to an increase in the reaction rate. Catalysts can increase the reaction rate by providing an alternative reaction pathway with a lower activation energy.

Step by step solution

01

Definition of Activation Energy

Activation energy, denoted as \(E_a\), is the minimum amount of energy required for a chemical reaction to proceed. It represents the energy barrier that must be overcome for the reactants to turn into products. In other words, even though a reaction might be energetically favorable, it will not happen instantaneously; there needs to be an input of energy to start the reaction process.
02

Role of Activation Energy in Reaction Rates

The activation energy plays a crucial role in determining the rate of a chemical reaction. The higher the activation energy, the slower the reaction rate, as fewer molecules will have the required energy to overcome the energy barrier. Conversely, a lower activation energy means that more molecules possess the necessary energy, and the reaction rate will be faster.
03

Temperature's Effect on Activation Energy

The relationship between temperature and activation energy is described by the Arrhenius equation, given by \[k = A \cdot e^{(-E_a/RT)}\], where \(k\) is the reaction rate constant, \(A\) is the pre-exponential factor, \(E_a\) is the activation energy, \(R\) is the gas constant, and \(T\) is the temperature in Kelvin. According to the equation, as the temperature increases, the reaction rate will also increase, because more molecules have enough energy to cross the activation energy barrier.
04

Catalysts and Activation Energy

Catalysts are substances that increase the rate of a chemical reaction without being consumed by the reaction itself. They work by providing an alternative reaction pathway with a lower activation energy, allowing more molecules to overcome the energy barrier and participate in the reaction. As a result, the reaction rate is increased even without changing other factors such as the concentrations of reactants or the temperature.

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Most popular questions from this chapter

For a reaction mechanism to be valid, the _______ rate law must agree with the _______ rate law.

The mechanism for the reaction of \(A_{2}\) with \(B\) is: Step \(1: \mathrm{A}_{2}+\mathrm{Y} \rightarrow \mathrm{AY}+\mathrm{A}\) (slow) Step \(2: \mathrm{A}+\mathrm{B} \rightarrow \mathrm{AB}\) (fast) Step 3: \(\mathrm{AY}+\mathrm{AB} \rightarrow \mathrm{Y}+\mathrm{A}_{2} \mathrm{~B}\) (fast) (a) Write the overall reaction that is occurring. (b) Which step determines the rate law for the reaction? (c) Write the rate law for the reaction. (d) What happens to the rate of the reaction when \(\left[\mathrm{A}_{2}\right]\) is doubled? (e) Which species is the catalyst? (f) Which species are reaction intermediates?

True or false? The orders in a rate law are equal to the balancing coefficients in the slowest elementary step in a mechanism.

The reaction \(\mathrm{A}+2 \mathrm{~B}+\mathrm{C} \rightarrow \mathrm{AB}_{2} \mathrm{C}\) has a rate that does not change when more \(C\) is added to the reaction flask. Suppose the overall reaction order is 2, and the reaction is first-order with respect to \(\mathrm{A}\). (a) Write the rate law for this reaction, (b) What is the order for reactant \(C ?\)

Why would decreasing the volume of a container in which a gas-phase reaction is taking place speed up the reaction?
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