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Ch.19 - Free Energy & Thermodynamics
Chapter 19, Problem 42c

Given the values of ΔH°rxn, ΔS°rxn, and T, determine ΔSuniv and predict whether or not each reaction is spontaneous. (Assume that all reactants and products are in their standard states.) c. ΔH°rxn = +95 kJ; ΔS°rxn = -157 J/K; T = 298 K

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Gibbs Free Energy

Gibbs Free Energy (G) is a thermodynamic potential that helps predict the spontaneity of a reaction at constant temperature and pressure. It is calculated using the equation ΔG = ΔH - TΔS, where ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy. A negative ΔG indicates a spontaneous reaction, while a positive ΔG suggests non-spontaneity.
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Entropy (ΔS)

Entropy (ΔS) is a measure of the disorder or randomness in a system. In the context of a chemical reaction, a positive ΔS indicates an increase in disorder, which favors spontaneity. Conversely, a negative ΔS suggests a decrease in disorder, which can hinder spontaneity. The change in entropy is crucial for determining the overall spontaneity of a reaction when combined with enthalpy changes.
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Enthalpy (ΔH)

Enthalpy (ΔH) is a measure of the total heat content of a system and reflects the energy absorbed or released during a reaction. A positive ΔH indicates that the reaction is endothermic, absorbing heat from the surroundings, while a negative ΔH indicates an exothermic reaction, releasing heat. The sign and magnitude of ΔH are essential for evaluating the energy changes that influence the spontaneity of a reaction in conjunction with entropy.
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