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Ch.19 - Free Energy & Thermodynamics
Tro - Chemistry: A Molecular Approach 6th Edition
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Tutti i libri di testoTro 6th EditionCh.19 - Free Energy & ThermodynamicsProblema 46
Capitolo 19, Problema 46

Calculate the change in Gibbs free energy for each of the sets of ΔH°rxn, ΔS°rxn, and T given in Problem 44. Predict whether or not each reaction is spontaneous at the temperature indicated. (Assume that all reactants and products are in their standard states.)

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1
Identify the formula for Gibbs free energy change: \( \Delta G^\circ = \Delta H^\circ - T \Delta S^\circ \).
Substitute the given values for \( \Delta H^\circ_{rxn} \), \( \Delta S^\circ_{rxn} \), and \( T \) into the formula.
Ensure that the units are consistent, typically converting \( \Delta S^\circ_{rxn} \) from J/mol·K to kJ/mol·K by dividing by 1000, if necessary.
Calculate \( \Delta G^\circ \) using the substituted values.
Determine spontaneity: if \( \Delta G^\circ < 0 \), the reaction is spontaneous; if \( \Delta G^\circ > 0 \), it is non-spontaneous.

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Gibbs Free Energy (G)

Gibbs free energy is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. It is defined by the equation G = H - TS, where H is enthalpy, T is temperature, and S is entropy. A negative change in Gibbs free energy (ΔG < 0) indicates that a reaction is spontaneous, while a positive change (ΔG > 0) suggests non-spontaneity.
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Gibbs Free Energy of Reactions

Enthalpy (ΔH°<sub>rxn</sub>)

Enthalpy change (ΔH°<sub>rxn</sub>) is the heat content change associated with a chemical reaction at standard conditions. It can be either exothermic (releasing heat, ΔH < 0) or endothermic (absorbing heat, ΔH > 0). The sign and magnitude of ΔH°<sub>rxn</sub> significantly influence the spontaneity of a reaction, as it contributes to the overall Gibbs free energy change.
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Enthalpy of Formation Example 1

Entropy (ΔS°<sub>rxn</sub>)

Entropy (ΔS°<sub>rxn</sub>) is a measure of the disorder or randomness in a system. In the context of a chemical reaction, an increase in entropy (ΔS > 0) generally favors spontaneity, as systems tend to evolve towards greater disorder. The relationship between entropy, enthalpy, and temperature is crucial for determining the spontaneity of reactions through the Gibbs free energy equation.
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Entropy and Physical Changes Example
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Fill in the blanks in the table. Both ΔH and ΔS refer to the system.

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