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UConn CHEM 1125Q - Gibbs Free Energy and the 3rd Law of Thermodynamics

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CHEM 1125Q 1st Edition Lecture 15 Outline of Last Lecture Ch. 14I. Standard Entropy, Entropy Changes, Qualitative Predictions, Entropy of SurroundingsOutline of Current Lecture Ch. 14II. 3rd Law of ThermodynamicsIII. Gibbs Free Energy ChangeIV. Standard Free Energy ChangeCurrent LectureII. 3rd Law of ThermodynamicsA. 3rd Law of Thermodynamicsa. The 3rd Law of thermodynamics states that a perfect crystalline substance, which is a theoretical substance only, has an entropy of 0 at Absolute Zero, which is a theoretical minimumb. As a substance’s temperature increases from Absolute Zero its entropy increasesIII. Gibbs Free Energy ChangeA. Gibbs Free Energy Changea. Gibbs free energy (G), known simply as free energy, expresses spontaneity directlyi. G = H – TSb. Since measurements on the surroundings are not often made, the useof the 2nd Law of Thermodynamics is limitedc. The change in free energy for a system is depicted by this state function:i. ΔG = ΔH – TΔSd. It is possible to predict spontaneity by using Gi. ΔG < 0 is spontaneousii. ΔG > 0 is not spontaneousiii. ΔG = 0 is at equilibriume. When ΔH is negative and ΔS is positive, the system is always spontaneousf. When ΔH is positive and ΔS is negative, the system is never spontaneousg. ΔG = 0 is the transition between spontaneity and non-spontaneityThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.IV. Standard Free Energy ChangeA. Standard Free Energy Changea. Standard free energy change, ΔG0, is used for a reaction that occurs under standard state conditionsi. Gases: 1atmii. Liquids: Pure liquidiii. Solids: Pure solidiv. Elements: The most stable allotropic form is at 1atm and 25 °Cv. Solutions: 1M concentrationb. ΔG0 = ΣΔGT0products – ΣΔGT0reactionc. ΔG and ΔH follow all of the same rules. Both are in kJ and both have values of 0 for elementsd. ΔS and S are temperature dependent. The only time that S is 0 is at Absolute


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UConn CHEM 1125Q - Gibbs Free Energy and the 3rd Law of Thermodynamics

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