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CHEM 204
Christopher Barrett

CHEM 204 03/18/2013 Lecture 26 Martin M. PHGY Tutor Entropy Recall: an exact number of joules per less and more likely outcomes. The universe wants an increase in entropy! Calculated similar to enthalpy Example chemical reaction: O 2(g) 2H 2(g) 2H O2, (g) Total number of particles decreased, so there is a decrease in entropy.  Q: Why does this reaction happen then if the universe wants an increase in entropy?  A: This negative entropy is only the entropy of the system. The surroundings actually increased their entropy. Consider the fact that the Δ f° of water is -286 kJ/mol. The reaction above made 2 moles of water, or -572 kJ. ( ) The overall entropy including the surroundings was +1590kJ for this reaction so it is very likely to happen. This total entropy above is Gibb's Free Energy. Derivation: Note: In step 2, we want to add the entropy of the surroundings so we put a negative sign to make the entropy positive. CHEM 204 03/18/2013 Lecture 26 Martin M. PHGY Tutor Gibb's Free Energy is the mirror opposite of total entropy. Any reaction is trying to increase its total entropy, and thus equivalently every reaction is trying to decrease the Gibbs
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