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## Discussion

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### Enthalpy, Entropy, Second Law of Thermodynamics

Reversibility a hypothetical idea; only applies to tiny changes

Definitions and calculations of entropy: DS = q

_{rev}/TEntropies of gases>entropies of liquids> entropies of solids

Third law of thermodynamics: S of perfect crystals at 0K = 0

Calculate entropy changes for phase changes

Learn definition of Second law of thermodynamics

Second law alone may be hard to apply in predicting equilibrium state of systems

### Enthalpy, Entropy, Second Law of Thermodynamics

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

- Intro
- Factors Affecting Equilibrium Constants
- State Functions: Enthalpy and Entropy
- Statistical Interpretation of Entropy
- Third Law of Thermodynamics
- Entropies of Gases, Liquids, and Solids
- Entropy Values from Enthalpy/Temperature
- Entropy Changes in Phase Changes
- Second Law of Thermodynamics
- Reactant Favored and Product Favored Equilibria
- Limitations of Applying the Second Law to Equilibria

- Intro 0:00
- Factors Affecting Equilibrium Constants 1:15
- Spontaneous Reaction
- Temperature Effects
- State Functions: Enthalpy and Entropy 6:17
- Example: Methane and Chlorine
- Hess's Law
- Entropy
- Statistical Interpretation of Entropy 13:24
- Boltzmann Entropy Equation
- Reversible Change
- Example: Water and Ice
- Third Law of Thermodynamics 20:06
- Nernst
- Entropies of Gases, Liquids, and Solids 23:16
- Example: Entropy Values
- Entropy Values from Enthalpy/Temperature 28:55
- Example: Water (Graph)
- Entropy Changes in Phase Changes 32:33
- Melting (Fusion)
- Example: Water Melting
- Second Law of Thermodynamics 34:21
- Example: Hydrogen and Oxygen
- Statement of Second Law (Spontaneous/Reversible)
- Reactant Favored and Product Favored Equilibria 41:10
- Reactant or Product Favored
- Converse
- Limitations of Applying the Second Law to Equilibria 46:57
- Delta S

0 answers

Post by KyungYeop Kim on July 9, 2013

Regarding a specific situation in which a nonspontaneous reaction under standard conditions becomes spontaneous at lower temperature, how can I describe this phenomenon in relation to enthalpy, entropy, and free energy? and how can I explain it in terms of temperature change? I've succeeded so far in determining that Î”G>0 since it's nonspontaneous under standard conditions, but what about Î”H and Î”S?

Given the equation = Î”G = Î”H*TÎ”S; I think the fact that temperature(T) can go either from positive to negative or negative to negative seems to confuse me. Are we assuming, in saying lowering temperature, that the T goes from negative(-) to negative(-)?

I know it's a complex problem, and I apologize if I'm asking too much, but I would like to know what the answer is and why. Thank you always!

2 answers

Last reply by: Dr. Harold Goldwhite

Thu May 9, 2013 11:53 AM

Post by Maimouna Louche on July 25, 2012

Thanks for the making your lessons easy to understand! ^^