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

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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).

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 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.

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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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Determine ΔG° for the reaction: Fe₂O₃(s) + 3 CO(g) → 2 Fe(s) + 3 CO₂(g) Use the following reactions with known ΔG°_rxnvalues:

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Consider the sublimation of iodine at 25.0 °C : I₂(s) → I₂(g) b. Find ΔG°_rxnat 25.0 °C under the following nonstandard conditions: i. P_I2 = 1.00 mmHg ii. P_I2 = 0.100 mmHg

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Consider the sublimation of iodine at 25.0 °C : I₂(s) → I₂(g) c. Explain why iodine spontaneously sublimes in open air at 25.0 °C

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Consider the evaporation of methanol at 25.0 °C : CH₃OH(l) → CH₃OH(g) a. Find ΔG°_r at 25.0 °C.

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