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Ch.18 - Free Energy and Thermodynamics
Tro - Chemistry: A Molecular Approach 4th Edition
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Tutti i libri di testoTro 4th EditionCh.18 - Free Energy and ThermodynamicsProblema 57
Capitolo 18, Problema 57

Find ΔS° for the formation of CH2Cl2(g) from its gaseous elements in their standard states. Rationalize the sign of ΔS°.

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Identify the reaction for the formation of CH2Cl2(g) from its gaseous elements: C(graphite) + 2H2(g) + 2Cl2(g) -> CH2Cl2(g).
Use the standard entropy values (S°) for each substance involved in the reaction. These values are typically found in a table of thermodynamic data.
Calculate the change in entropy (ΔS°) for the reaction using the formula: ΔS° = ΣS°(products) - ΣS°(reactants).
Substitute the standard entropy values into the formula to find ΔS°.
Rationalize the sign of ΔS°: Consider the change in the number of moles of gas and the complexity of the molecules involved. Formation of CH2Cl2(g) from simpler gaseous elements may lead to a decrease in entropy due to a decrease in the number of gas molecules.

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Standard Entropy (ΔS°)

Standard entropy (ΔS°) is a measure of the disorder or randomness of a system at standard conditions (1 bar, 25°C). It quantifies the amount of energy unavailable for doing work due to the dispersal of energy in a system. A positive ΔS° indicates an increase in disorder, while a negative ΔS° suggests a decrease in disorder.
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Standard Molar Entropy

Formation Reaction

A formation reaction is a chemical reaction in which one mole of a compound is formed from its constituent elements in their standard states. For example, the formation of dichloromethane (CH2Cl2) involves combining carbon, hydrogen, and chlorine gases. The standard enthalpy and entropy changes for this reaction are crucial for calculating thermodynamic properties.
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Enthalpy of Formation

Gibbs Free Energy and Spontaneity

Gibbs free energy (G) combines enthalpy and entropy to determine the spontaneity of a reaction at constant temperature and pressure. The change in Gibbs free energy (ΔG) is given by the equation ΔG = ΔH - TΔS. A negative ΔG indicates a spontaneous process, while the sign of ΔS helps rationalize whether the reaction increases or decreases disorder, influencing the overall spontaneity.
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Gibbs Free Energy of Reactions
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