Gibb’s Free Energy & Temperature
Related Examples and Practice Problems
Additional Worked Out Examples/ Practice
Identifying classification types: Differentiation between elements, compounds or mixtures and homogeneous and heterogenous mixtures
Separation techniques: Selected and explaining limitation of appropriate separation
Relating Properties to Composition: Predicting classification based on descriptive properties
Topic Summary & Highlights
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Core Concept
Ionic compounds are composed of a cation and anion. The cation is typically a metal, and the anion is usually a nonmetal or a polyatomic ion (a group of atoms with an overall charge). If the compound contains a metal it is a good sign that it can be considered an ionic compound.
Practice Tips
The spontaneity of a reaction depends on the relationship between ΔH, T, and ΔS.
Temperature plays a critical role in determining ΔG, especially when ΔH and ΔS have the same sign.
Understanding $T_{\text{crit}}$ helps predict when a reaction becomes spontaneous or non-spontaneous.
The fundamental equation for Gibbs Free Energy is:
ΔG=ΔH−TΔS\Delta G = \Delta H - T \Delta SΔG=ΔH−TΔS
Where:
ΔG\Delta GΔG: Gibbs Free Energy change (kJ/mol\text{kJ/mol}kJ/mol or J/mol\text{J/mol}J/mol).
ΔH\Delta HΔH: Enthalpy change (kJ/mol\text{kJ/mol}kJ/mol).
TTT: Absolute temperature (Kelvin).
ΔS\Delta SΔS: Entropy change (J/K\cdotpmol\text{J/K·mol}J/K\cdotpmol).
Temperature Dependence of ΔG\Delta GΔG
The spontaneity of a reaction (ΔG\Delta GΔG) depends on the interplay between ΔH\Delta HΔH, ΔS\Delta SΔS, and TTT:
Enthalpy (ΔH\Delta HΔH): Represents heat absorbed or released.
ΔH<0\Delta H < 0ΔH<0: Exothermic reactions.
ΔH>0\Delta H > 0ΔH>0: Endothermic reactions.
Entropy (ΔS\Delta SΔS): Represents disorder or energy dispersal.
ΔS>0\Delta S > 0ΔS>0: Increased disorder (favors spontaneity).
ΔS<0\Delta S < 0ΔS<0: Decreased disorder.
The temperature term (TΔST \Delta STΔS) determines whether entropy or enthalpy dominates at different temperatures.
Key Scenarios
The sign of ΔG\Delta GΔG depends on ΔH\Delta HΔH and ΔS\Delta SΔS:
ΔH\Delta HΔHΔS\Delta SΔSEffect at Low TTTEffect at High TTTNegativePositiveSpontaneous (ΔG<0\Delta G < 0ΔG<0)Spontaneous (ΔG<0\Delta G < 0ΔG<0)NegativeNegativeSpontaneous (ΔG<0\Delta G < 0ΔG<0)Non-spontaneous (ΔG>0\Delta G > 0ΔG>0)PositivePositiveNon-spontaneous (ΔG>0\Delta G > 0ΔG>0)Spontaneous (ΔG<0\Delta G < 0ΔG<0)PositiveNegativeNon-spontaneous (ΔG>0\Delta G > 0ΔG>0)Non-spontaneous (ΔG>0\Delta G > 0ΔG>0)
Critical Temperature (TcritT_{\text{crit}}Tcrit)
Definition: The temperature at which ΔG=0\Delta G = 0ΔG=0, meaning the reaction is at equilibrium.
Calculation: Tcrit=ΔHΔST_{\text{crit}} = \frac{\Delta H}{\Delta S}Tcrit=ΔSΔH
If T>TcritT > T_{\text{crit}}T>Tcrit, the reaction's spontaneity depends on entropy (ΔS\Delta SΔS).
If T<TcritT < T_{\text{crit}}T<Tcrit, the reaction's spontaneity depends on enthalpy (ΔH\Delta HΔH).