Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium

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McMurry 8th Edition

Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium

Problema 132

Capitolo 18, Problema 132

Tell whether reactions with the following values of ΔH and ΔS are spontaneous or nonspontaneous and whether they are exothermic or endothermic. (a) ΔH = - 48 kJ; ΔS = + 135 J>K at 400 K (b) ΔH = - 48 kJ; ΔS = - 135 J>K at 400 K (c) ΔH = + 48 kJ; ΔS = + 135 J>K at 400 K (d) ΔH = + 48 kJ; ΔS = - 135 J>K at 400 K

Guida verificata passo dopo passo

Step 1: Recall the Gibbs free energy equation: \( \Delta G = \Delta H - T \Delta S \). This equation helps determine the spontaneity of a reaction.

Step 2: Convert \( \Delta S \) from J/K to kJ/K by dividing by 1000, since \( \Delta H \) is given in kJ.

Step 3: For each scenario, substitute the given values of \( \Delta H \), \( \Delta S \), and \( T \) into the Gibbs free energy equation to calculate \( \Delta G \).

Step 4: Determine spontaneity: If \( \Delta G < 0 \), the reaction is spontaneous; if \( \Delta G > 0 \), the reaction is nonspontaneous.

Step 5: Determine if the reaction is exothermic or endothermic: If \( \Delta H < 0 \), the reaction is exothermic; if \( \Delta H > 0 \), the reaction is endothermic.

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Gibbs Free Energy

Gibbs Free Energy (G) is a thermodynamic potential that helps predict the spontaneity of a reaction at constant temperature and pressure. The change in Gibbs Free Energy (ΔG) 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 indicates nonspontaneity.

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01:51

Gibbs Free Energy of Reactions

Enthalpy (ΔH)

Enthalpy (ΔH) is a measure of the total heat content of a system. It can be classified as exothermic (ΔH < 0) when heat is released during a reaction, or endothermic (ΔH > 0) when heat is absorbed. The sign of ΔH is crucial for determining the energy changes associated with a reaction and influences the overall spontaneity when combined with entropy changes.

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Enthalpy of Formation

Entropy (ΔS)

Entropy (ΔS) is a measure of the disorder or randomness in a system. A positive ΔS indicates an increase in disorder, which generally favors spontaneity, while a negative ΔS suggests a decrease in disorder, which can hinder spontaneity. The interplay between ΔS and ΔH at a given temperature is essential for determining whether a reaction will occur spontaneously.

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Entropy in Thermodynamics

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