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Chapter 10: Problem 19

What information is needed to be certain that a chemical reaction is nonspontaneous?

Short Answer

Expert verified
The information needed to be certain that a chemical reaction is nonspontaneous involves its Gibbs free energy change (\( \Delta G \)), which should be positive. Other relevant data may include knowledge about the system's enthalpy change (\( \Delta H \)) and entropy change (\( \Delta S \)), and how they contribute to the value of \( \Delta G \).

Step by step solution

01

Define Nonspontaneous Reactions

Nonspontaneous reactions are chemical reactions that do not proceed on their own unless energy is supplied. These reactions are energetically unfavorable, which means they have positive changes in Gibbs free energy (\( \Delta G > 0 \)).
02

Understand Gibbs Free Energy

The key to determining if a reaction is spontaneous or nonspontaneous lies in the change of Gibbs free energy, \( \Delta G \). Gibbs free energy is used to measure the maximum reversible work that a system can perform at constant temperature and pressure. When \( \Delta G \) is positive, the reaction is nonspontaneous, and when \( \Delta G \) is negative, the reaction is spontaneous.
03

Understanding the Relationship with Entropy and Enthalpy

The Gibbs free energy change (\( \Delta G \)) is related to the enthalpy change (\( \Delta H \)) and the entropy change (\( \Delta S \)) at a constant temperature. The relationship is given by the equation \( \Delta G = \Delta H - T\Delta S \), where \( T \) is the absolute temperature. For nonspontaneous reactions, either the system is endothermic (\( \Delta H > 0 \)) with a decrease in entropy (\( \Delta S < 0 \)), or the decrease in entropy outweighs the exothermic nature of the reaction, causing \( \Delta G \) to be positive.

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Most popular questions from this chapter

At high temperatures, does enthalpy or entropy have a greater effect on a reaction's Gibbs energy?

Graphing Calculator Calculating the Gibbs-Energy Change The graphing calculator can run a program that calculates the Gibbs-energy change, given the temperature, \(T\) , change in enthalpy \(\Delta H,\) and change in entropy, \(\Delta S .\) Given that the temperature is 298 \(\mathrm{K}\) , the change in enthalpy is 131.3 \(\mathrm{kJ} / \mathrm{mol}\) , and the change in entropy is \(0.134 \mathrm{kJ} /(\mathrm{mol} \cdot \mathrm{K}),\) you can calculate Gibbs-energy change in kilojoules per mole. Then use the program to make calculations. Go to Appendix C. If you are using a TI-83 Plus, you can download the program ENERGY data and run the application as directed. If you are using another calculator, your teacher will provide you with keystrokes and data sets to use. After you have run the program, answer the following questions. \begin{equation} \begin{array}{l}{\text { a. What is the Gibbs-energy change given a }} \\\ {\text { temperature of } 300 \mathrm{K}, \text { a change in enthalpy }} \\\ {\text { of } 132 \mathrm{kJ} / \mathrm{mol} \text { and a change in entropy of }} \\ {0.086 \mathrm{kJ} / /(\mathrm{mol} \cdot \mathrm{K}) ?}\\\\{\text { b. What is the Gibbs-energy change given a }} \\ {\text { temperature of } 288 \mathrm{K}, \text { a change in enthalpy }} \\ {\text { of } 115 \mathrm{kJ} / \mathrm{mol} \text { and a change in entropy of }} \\ {0.113 \mathrm{kJ} /(\mathrm{mol} \cdot \mathrm{K}) ?}\\\\{\text { c. What is the Gibbs-energy change given a }} \\ {\text { temperature of } 298 \mathrm{K} \text { , a change in enthalpy }} \\ {\text { of } 181 \mathrm{kJ} / \mathrm{mol} \text { and a change in entropy of }} \\ {0.135 \mathrm{kJ} /(\mathrm{mol} \cdot \mathrm{K}) ?}\end{array} \end{equation}

What is entropy?

What influences the changes in molar enthalpy?

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