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Ch.18 - Free Energy and Thermodynamics
Chapter 18, Problem 67

Determine ΔG° for the reaction: Fe2O3(s) + 3 CO(g) → 2 Fe(s) + 3 CO2(g) Use the following reactions with known ΔG°rxn values:
2 Fe(s) + 3/2 O2(g) → Fe2O3(s) ΔG°rxn = -742.2 kJ
CO(g) + 12 O2( g) → CO2(g) ΔG°rxn = -257.2 kJ

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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. A negative ΔG° indicates that a reaction is spontaneous, while a positive ΔG° suggests non-spontaneity. Understanding ΔG° is crucial for predicting the favorability of chemical reactions.
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Gibbs Free Energy of Reactions

Standard Reaction Gibbs Free Energy (ΔG°rxn)

Standard Reaction Gibbs Free Energy (ΔG°rxn) refers to the change in Gibbs Free Energy for a reaction under standard conditions (1 bar pressure, 298 K temperature). It is calculated using the Gibbs Free Energy values of the reactants and products. This concept is essential for determining the spontaneity and equilibrium of reactions, as seen in the provided reactions.
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Hess's Law

Hess's Law states that the total enthalpy change for a reaction is the sum of the enthalpy changes for the individual steps, regardless of the pathway taken. This principle can be applied to Gibbs Free Energy calculations, allowing us to combine known ΔG°rxn values from multiple reactions to find the ΔG° for a target reaction. It is a powerful tool in thermodynamics for deriving reaction energetics.
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Related Practice
Open Question
Is the question formulated correctly? If not, please correct it. Here is the question: 'Consider the reaction: 2 NO( g) + O2( g) → 2 NO2( g). Estimate ΔG° for this reaction at each temperature and predict whether or not the reaction is spontaneous, assuming that ΔH° and ΔS° do not change significantly within the given temperature range. a. 298 K b. 855 K.'
Textbook Question

Consider the reaction: 2 NO(g) + O2(g) → 2 NO2(g) Estimate ΔG° for this reaction at each temperature and predict whether or not the reaction is spontaneous. (Assume that ΔH° and ΔS° do not change too much within the given temperature range.) b. 715 K

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Open Question
Consider the reaction: CaCO3(s) → CaO(s) + CO2(g). Estimate ΔG° for this reaction at each temperature and predict whether or not the reaction is spontaneous. (Assume that ΔH° and ΔS° do not change too much within the given temperature range.) a. 298 K b. 1055 K c. 1455 K.
Open Question
Calculate ΔG°rxn for the reaction: CaCO3(s) → CaO(s) + CO2(g). Use the following reactions and given ΔG°rxn values: Ca(s) + CO2(g) + 1/2 O2(g) → CaCO3(s) ΔG°rxn = -734.4 kJ, 2 Ca(s) + O2(g) → 2 CaO(s) ΔG°rxn = -1206.6 kJ.
Open Question
Consider the sublimation of iodine at 25.0 °C: I2(s) → I2(g). a. Find ΔG°rxn at 25.0 °C.
Textbook Question

Consider the sublimation of iodine at 25.0 °C : I2(s) → I2(g) b. Find ΔG°rxn at 25.0 °C under the following nonstandard conditions: i. PI2 = 1.00 mmHg ii. PI2 = 0.100 mmHg

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