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Ch.18 - Free Energy and Thermodynamics
Tro - Chemistry: A Molecular Approach 4th Edition
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Tutti i libri di testoTro 4th EditionCh.18 - Free Energy and ThermodynamicsProblema 69b
Capitolo 18, Problema 69b

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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Identify the reaction: I_2(s) \(\rightarrow\) I_2(g).
Use the equation \( \Delta G = \Delta G^\circ + RT \ln Q \) to find \( \Delta G \) under nonstandard conditions.
Calculate the reaction quotient \( Q \) using \( Q = \frac{P_{I_2}}{P^\circ} \), where \( P^\circ = 1 \text{ atm} \).
For \( P_{I_2} = 1.00 \text{ mmHg} \), convert to atm and calculate \( Q \).
For \( P_{I_2} = 0.100 \text{ mmHg} \), convert to atm and calculate \( Q \).

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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 crucial for predicting the spontaneity of a reaction; a negative ΔG indicates a spontaneous process, while a positive ΔG suggests non-spontaneity. The relationship between ΔG, enthalpy (ΔH), and entropy (ΔS) is given by the equation ΔG = ΔH - TΔS.
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Gibbs Free Energy of Reactions

Standard State and Nonstandard Conditions

The standard state of a substance is defined as its most stable form at 1 bar (or 1 atm) and a specified temperature, typically 25 °C. Nonstandard conditions refer to any conditions that deviate from these standard states, such as different pressures or concentrations. In the context of the question, the partial pressures of iodine gas (PI2) at 1.00 mmHg and 0.100 mmHg are examples of nonstandard conditions that affect the calculation of ΔG.
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Standard Reduction Potentials

Van 't Hoff Equation

The Van 't Hoff equation relates the change in the equilibrium constant (K) of a reaction to the change in temperature and is often used to derive the Gibbs Free Energy under nonstandard conditions. It can be expressed as ΔG = ΔG° + RT ln(Q), where Q is the reaction quotient. This equation allows for the calculation of ΔG at varying pressures or concentrations, which is essential for solving the given problem regarding the sublimation of iodine.
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Van der Waals Equation
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