Consider the sublimation of iodine at 25.0 °C: I2(s) → I2(g). a. Find ΔG°rxn at 25.0 °C.

Name: Chemistry: A Molecular Approach
Author: Tro
ISBN: 9780134112831

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Identify the relevant thermodynamic equation: \( \Delta G^\circ_{\text{rxn}} = \Delta H^\circ - T\Delta S^\circ \).

Look up the standard enthalpy change (\( \Delta H^\circ \)) and the standard entropy change (\( \Delta S^\circ \)) for the sublimation of iodine from a reliable source, such as a chemistry textbook or database.

Convert the temperature from Celsius to Kelvin by adding 273.15 to the Celsius temperature: \( T = 25.0 + 273.15 \).

Substitute the values of \( \Delta H^\circ \), \( T \) (in Kelvin), and \( \Delta S^\circ \) into the equation \( \Delta G^\circ_{\text{rxn}} = \Delta H^\circ - T\Delta S^\circ \).

Perform the calculation to find \( \Delta G^\circ_{\text{rxn}} \), ensuring that the units are consistent (e.g., convert \( \Delta S^\circ \) from J/mol·K to kJ/mol·K if necessary).

주요 개념

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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 a crucial concept in predicting the spontaneity of a reaction; a negative ΔG indicates a spontaneous process, while a positive ΔG suggests non-spontaneity. The standard Gibbs free energy change (ΔG°) is calculated under standard conditions, providing a reference point for reactions.

Sublimation

Sublimation is the phase transition in which a substance changes directly from a solid to a gas without passing through the liquid phase. This process occurs when the molecules in the solid gain enough energy to overcome intermolecular forces and enter the gaseous state. Understanding sublimation is essential for calculating the Gibbs free energy change for the reaction involving iodine, as it directly relates to the enthalpy and entropy changes during the phase transition.

Standard State Conditions

Standard state conditions refer to a set of specific conditions (usually 1 bar of pressure and a specified temperature, often 25 °C) under which thermodynamic measurements are made. These conditions allow for the comparison of thermodynamic data across different substances. When calculating ΔG°rxn, it is important to use standard state values for enthalpy (ΔH°) and entropy (ΔS°) to ensure accurate results for the reaction at the specified temperature.