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Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium
Chapter 18, Problem 141b

Consider the unbalanced equation: (b) Use the data in Appendix B and ΔG°f for IO3-(aq)= -128.0 kJ/mol to calculate ΔG° for the reaction at 25 °C.

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insert step 1> Identify the balanced chemical equation for the reaction.
insert step 2> Use the standard Gibbs free energy of formation (ΔG°f) values from Appendix B for each reactant and product in the balanced equation.
insert step 3> Calculate the ΔG° for the reaction using the formula: ΔG° = Σ(ΔG°f of products) - Σ(ΔG°f of reactants).
insert step 4> Substitute the given ΔG°f value for IO_3^-(aq) and the values from Appendix B into the equation.
insert step 5> Perform the arithmetic to find the ΔG° for the reaction at 25 °C.

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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.
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Standard Gibbs Free Energy of Formation (ΔG°f)

The Standard Gibbs Free Energy of Formation (ΔG°f) is the change in Gibbs free energy when one mole of a compound is formed from its elements in their standard states. This value is essential for calculating the ΔG of a reaction, as it allows for the determination of the energy changes associated with the formation of reactants and products.
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Reaction Quotient and Equilibrium

The reaction quotient (Q) is a measure of the relative concentrations of products and reactants at any point in a reaction. At equilibrium, Q equals the equilibrium constant (K). Understanding how ΔG relates to Q and K is vital for predicting the direction of a reaction and calculating the ΔG under non-standard conditions.
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