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Chapter 18: Problem 16

Why is it more convenient to predict the direction of a reaction in terms of \(\Delta G_{\text {sys }}\) instead of \(\Delta S_{\text {univ }}\) ? Under what conditions can \(\Delta G_{\text {sys }}\) be used to predict the spontaneity of a reaction?

Short Answer

Expert verified
It's more convenient to use \(\Delta G_{\text{sys}}\) because it measures changes within the system which is more feasible compared to measuring the universe's entropy change. \(\Delta G_{\text{sys}}\) can effectively predict spontaneity if it's negative, which denotes a spontaneous reaction, positive then it's not spontaneous, and if it equals zero, the reaction is at equilibrium.

Step by step solution

01

Understanding the Variables

\(\Delta G_{\text{sys}}\) refers to the change in Gibbs Free Energy of the system (reactants and products), while \(\Delta S_{\text{univ}}\) refers to the change in entropy of the universe (system plus surroundings). Gibbs free energy is the usable (or free) energy available to do work, while entropy is a measure of disorder in a system.
02

Convenience of \(\Delta G_{\text{sys}}\)

It is easier to measure changes within the system (the reactants and products), which is what \(\Delta G_{\text{sys}}\) represents, as we can directly control and influence the reactants and products. Measuring the whole universe's entropy change is practically impossible, as it includes the system and the surroundings.
03

Conditions for Predicting Spontaneity

A practical predictor of spontaneity is whether \(\Delta G_{\text{sys}}\) is negative. When \(\Delta G_{\text{sys}}\) is negative, reaction is spontaneous in forward direction. If \(\Delta G_{\text{sys}}\) is positive, it's not spontaneous (though it might still happen if energy is added to the system). If \(\Delta G_{\text{sys}}\) equals zero, the reaction is at equilibrium.

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Most popular questions from this chapter

Under what conditions does a substance have a standard entropy of zero? Can a substance ever have a negative standard entropy?

The equilibrium constant \(K_{P}\) for the reaction $$ \mathrm{CO}(g)+\mathrm{Cl}_{2}(g) \rightleftharpoons \mathrm{COCl}_{2}(g) $$ is \(5.62 \times 10^{35}\) at \(25^{\circ} \mathrm{C}\). Calculate \(\Delta G_{\mathrm{f}}^{\circ}\) for \(\mathrm{COCl}_{2}\) at \(25^{\circ} \mathrm{C}\).

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Crystallization of sodium acetate from a supersaturated solution occurs spontaneously (see p. 426). What can you deduce about the signs of \(\Delta S\) and \(\Delta H ?\)

What is a coupled reaction? What is its importance in biological reactions?
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