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Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium
McMurry - Chemistry 8th Edition
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Tutti i libri di testoMcMurry 8th EditionCh.18 - Thermodynamics: Entropy, Free Energy & EquilibriumProblema 5
Capitolo 18, Problema 5

Magnesium m#etal has ΔHfusion = 9.037 kJ>mol and ΔSfusion = 9.79 J>1K mol2. What is the melting point of magnesium in °C? (LO 11.4) (a) 0.923 °C (b) 923 °C (c) 650 °C (d) 1.08 * 103 °C

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Identify the given values: ΔH_fusion = 9.037 kJ/mol and ΔS_fusion = 9.79 J/(K mol).
Convert ΔH_fusion from kJ/mol to J/mol for consistency in units. Recall that 1 kJ = 1000 J.
Use the formula for the melting point (T_m) based on thermodynamics: T_m = ΔH_fusion / ΔS_fusion.
Plug the converted ΔH_fusion and ΔS_fusion values into the formula to calculate T_m in Kelvin.
Convert the temperature from Kelvin to Celsius using the formula: °C = K - 273.15.

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Gibbs Free Energy

Gibbs Free Energy (G) is a thermodynamic potential that helps predict the direction of chemical reactions and phase changes. It combines enthalpy (ΔH) and entropy (ΔS) into a single value, allowing us to determine if a process is spontaneous at constant temperature and pressure. The relationship is given by the equation ΔG = ΔH - TΔS, where T is the temperature in Kelvin.
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Gibbs Free Energy of Reactions

Phase Change and Melting Point

The melting point of a substance is the temperature at which it transitions from solid to liquid. This process involves a change in enthalpy (ΔHfusion) and entropy (ΔSfusion). At the melting point, the Gibbs Free Energy change (ΔG) is zero, indicating that the solid and liquid phases are in equilibrium.
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Boiling Point and Melting Point

Calculating Melting Point

To find the melting point of magnesium, we can rearrange the Gibbs Free Energy equation to solve for temperature: T = ΔHfusion / ΔSfusion. By substituting the given values of ΔHfusion and ΔSfusion into this equation, we can calculate the melting point in Kelvin and then convert it to Celsius by subtracting 273.15.
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04:29
Boiling Point and Melting Point
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