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Ch.19 - Chemical Thermodynamics
Brown - Chemistry: The Central Science 14th Edition
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Tutti i libri di testoBrown 14th EditionCh.19 - Chemical ThermodynamicsProblema 95a
Capitolo 19, Problema 95a

Consider the following three reactions: (i) Ti(s) + 2 Cl2(g) → TiCl4(1g) (a) For each of the reactions, use data in Appendix C to calculate ΔH°, ΔG°, K, and ΔS ° at 25 °C.

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Identify the standard enthalpies of formation (ΔHf°) for each reactant and product from Appendix C. For the reaction Ti(s) + 2 Cl2(g) → TiCl4(l), find the ΔHf° values for Ti(s), Cl2(g), and TiCl4(l).
Calculate the standard enthalpy change (ΔH°) for the reaction using the formula: ΔH° = ΣΔHf°(products) - ΣΔHf°(reactants). Plug in the values you found for each substance.
Identify the standard Gibbs free energy of formation (ΔGf°) for each reactant and product from Appendix C. Use these values to calculate the standard Gibbs free energy change (ΔG°) for the reaction using the formula: ΔG° = ΣΔGf°(products) - ΣΔGf°(reactants).
Calculate the standard entropy change (ΔS°) for the reaction using the formula: ΔS° = ΣS°(products) - ΣS°(reactants). Use the standard molar entropy values (S°) from Appendix C for each reactant and product.
Determine the equilibrium constant (K) at 25 °C using the relationship between ΔG° and K, which is given by the equation: ΔG° = -RT ln(K), where R is the gas constant (8.314 J/mol·K) and T is the temperature in Kelvin (298 K for 25 °C). Solve for K.

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Thermodynamics

Thermodynamics is the study of energy transformations and the relationships between heat, work, and energy. In chemical reactions, it helps determine the changes in enthalpy (ΔH°), Gibbs free energy (ΔG°), and entropy (ΔS°). Understanding these concepts is crucial for predicting the spontaneity and equilibrium of reactions.
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First Law of Thermodynamics

Gibbs Free Energy

Gibbs free energy (G) is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. The change in Gibbs free energy (ΔG°) indicates whether a reaction is spontaneous (ΔG° < 0) or non-spontaneous (ΔG° > 0) under standard conditions.
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Gibbs Free Energy of Reactions

Equilibrium Constant (K)

The equilibrium constant (K) is a dimensionless value that expresses the ratio of the concentrations of products to reactants at equilibrium for a given reaction at a specific temperature. It is related to the Gibbs free energy change (ΔG°) by the equation ΔG° = -RT ln(K), where R is the gas constant and T is the temperature in Kelvin.
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Equilibrium Constant K
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Using the data in Appendix C and given the pressures listed, calculate Kp and ΔG for each of the following reactions:

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Consider the following three reactions: (i) Ti(s) + 2 Cl2(g) → TiCl4(1g) (ii) C2H6(g) + 7 Cl2(g) → 2 CCl4(g) + 6 HCl(g) (iii) BaO(s) + CO2(g) → BaCO3(s) (c) For each of the reactions, predict the manner in which the change in free energy varies with an increase in temperature.

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Consider the following three reactions: (i) Ti(s) + 2 Cl2(g) → TiCl4(1g) (ii) C2H6(g) + 7 Cl2(g) → 2 CCl4(g) + 6 HCl(g) (iii) BaO(s) + CO2(g) → BaCO3(s) (b) Which of these reactions are spontaneous under standard conditions at 25 °C?

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(c) In general, under which condition is ΔG°f more positive (less negative) than ΔH°f ? (i) When the temperature is high, (ii) when the reaction is reversible, (iii) when ΔS°f is negative.

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