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Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium
Chapter 18, Problem 40

Assuming that gaseous reactants and products are present at 1 atm partial pressure, which of the following reactions are spontaneous in the forward direction? (a) (b) (c) (d)

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insert step 1: Identify the reactions and their respective Gibbs free energy changes (ΔG) if provided.
insert step 2: Recall that a reaction is spontaneous in the forward direction if ΔG is negative.
insert step 3: If ΔG is not provided, consider using the equation ΔG = ΔH - TΔS, where ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy.
insert step 4: Evaluate the sign of ΔG for each reaction. If ΔG is negative, the reaction is spontaneous in the forward direction.
insert step 5: Conclude which reactions are spontaneous based on the sign of ΔG for each reaction.

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Key Concepts

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

Gibbs Free Energy

Gibbs Free Energy (G) is a thermodynamic potential that helps predict the spontaneity of a reaction at constant temperature and pressure. A reaction is spontaneous in the forward direction if the change in Gibbs Free Energy (ΔG) is negative. This concept is crucial for determining whether a reaction will occur without external input.
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Le Chatelier's Principle

Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the system shifts in a direction that counteracts the change. This principle is important for understanding how changes in pressure, temperature, or concentration can affect the spontaneity of reactions involving gaseous reactants and products.
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Reaction Quotient (Q) and Equilibrium Constant (K)

The Reaction Quotient (Q) is a measure of the relative concentrations of reactants and products at any point in a reaction, while the Equilibrium Constant (K) describes the ratio at equilibrium. Comparing Q to K helps determine the direction of spontaneity: if Q < K, the reaction proceeds forward; if Q > K, it shifts backward. This concept is essential for analyzing the spontaneity of reactions under given conditions.
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