CHEM
Lect+18+08

# Lect+18+08 - Gibbs Free Energy Changes and...

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Gibbs Free Energy Changes and Thermodynamics/Chemical Equilibrium 2200 G ° = H ° - T S ° Calculating G ° Chapter 14 Chemical Equilibrium Mass Action Laws Thermodynamic equilibrium in Ideal Gases Thermodynamic equilibrium in Ideal Solutions Reaction involving multiple phases Multiple equilibria

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Gibbs Free Energy and Phase Transitions Phase transitions(pt) at the phase transition temperature can be reversible G= H pt - T pt S pt = H pt - T pt ( H pt /T pt ) = 0 Phase transitions NOT at the phase transition temperature cannot be reversible Super cooled water is water cooled below 273.15K. Super cooled water will freeze spontaneously when nucleated What is G for this freezing process?? Greater than 0 Equal to 0 Less than 0
Gibbs Free Energy for solidification of water

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Gibbs Free Energy and Chemical Reactions Standard Gibbs Free Energies for chemical compounds are tabulated and can be used to calculate standard free energies of chemical reactions Gibbs Free Energy is a state function so linear scaling applies just as was the case for standard enthalpies
Gibbs Free Energy and Chemical Reactions 2200 G ° = H ° - T S ° Gibbs Free Energy depends on H ° and - T S ° With increasing temperature the importance of the S ° term increases linearly If H ° is negative and S ° is positive then G ° will be negative and the reaction will be spontaneous at all temperatures If H ° is positive and S ° is positive then the sign of G ° depends on temperature. The reaction will be spontaneous only over a limited temperature range If H ° is negative and S ° is negative then the sign of G ° depends on temperature. The reaction will be spontaneous only over a limited temperature range

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Factors which make up Free Energy Positive S is favorable Negative H (Exothermic) is favorable Negative G is favorable (spontaneous)
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