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Ch.18 - Free Energy and Thermodynamics
Chapter 18, Problem 72

Consider the reaction: CO2(g) + CCl4(g) ⇌ 2 COCl2(g) Calculate ΔG for this reaction at 25 °C under the following conditions: i. PCO2 = 0.112 atm ii. PCCl4 = 0.174 atm iii. PCOCl2 = 0.744 atm

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Key Concepts

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

Gibbs Free Energy (ΔG)

Gibbs Free Energy (ΔG) is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. It is a crucial concept in predicting the spontaneity of a reaction; a negative ΔG indicates that a reaction can occur spontaneously, while a positive ΔG suggests non-spontaneity. The relationship between ΔG, enthalpy, and entropy is given by the equation ΔG = ΔH - TΔS.
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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. For the reaction CO2(g) + CCl4(g) ⇌ 2 COCl2(g), K can be calculated using the partial pressures of the gases involved. Understanding K is essential for calculating ΔG, as the relationship ΔG = ΔG° + RT ln(Q) connects the standard Gibbs free energy change (ΔG°) to the reaction quotient (Q) and K.
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Reaction Quotient (Q)

The reaction quotient (Q) is a measure of the relative amounts of products and reactants present in a reaction at any point in time, calculated using the same expression as the equilibrium constant (K). It helps determine the direction in which a reaction will proceed to reach equilibrium. If Q < K, the reaction will shift to the right (toward products), while if Q > K, it will shift to the left (toward reactants). In this question, Q is calculated using the given partial pressures.
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