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Chapter 13: Problem 4

The energy released by the reaction \(\mathrm{A} \rightarrow \mathrm{B}\) is \(400 \mathrm{~kJ} / \mathrm{mol}\). (a) What is \(\Delta E_{\text {forward } \mathrm{rxn}}\) ? (b) What is \(\Delta E_{\text {reverse rxn }}\) ?

Short Answer

Expert verified
(a) The change in energy, ΔE, for the forward reaction is -400 kJ/mol. (b) The change in energy, ΔE, for the reverse reaction is 400 kJ/mol.

Step by step solution

01

Part (a): Find ΔE for the forward reaction

For the forward reaction A → B, by definition, the energy released is given as negative of the change in energy ΔE. That is, -ΔE = Energy released. We have the energy released as 400 kJ/mol. So, -ΔE = 400 kJ/mol. Now we can find ΔE as: ΔE = -400 kJ/mol Thus, the change in energy, ΔE, for the forward reaction is -400 kJ/mol.
02

Part (b): Find ΔE for the reverse reaction

The reverse reaction can be represented as B → A. Since the energy released in the forward reaction A → B is 400 kJ/mol, in the reverse reaction B → A the energy is absorbed instead. This means the change in energy ΔE for the reverse reaction is positive, and equal in magnitude to that of the forward reaction. Thus, the change in energy, ΔE, for the reverse reaction is 400 kJ/mol.

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Most popular questions from this chapter

What is the relationship between the rate of a reaction and the value of \(E_{\mathrm{a}}\) for the reaction?

A reaction is exothermic, with \(\Delta E_{\mathrm{rxn}}=-40 \mathrm{~kJ}\), and the transition state is \(20 \mathrm{~kJ}\) higher in energy than the reactants. Sketch a reaction-energy profile consistent with this information, complete with labels for the distances representing \(\Delta E_{\mathrm{rxn}}\) and \(E_{\mathrm{a}} .\)

What do we mean by activation energy?

What is the rule of thumb for how reaction rate changes as the temperature changes?

Reactions go faster when heated. Astudent claims this is because as temperature increases, the activation energy \(E_{\mathrm{a}}\) for a reaction decreases. Is this student correct or incorrect? If incorrect, then explain what happens to \(E_{\mathrm{a}}\) upon heating a reaction.
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