Thermodynamics CHEM 1332
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This 3 page Class Notes was uploaded by Mythri Partha on Friday April 15, 2016. The Class Notes belongs to CHEM 1332 at University of Houston taught by Simon Bott in Spring 2016. Since its upload, it has received 16 views. For similar materials see Fundamentals of Chemistry 2 in Chemistry at University of Houston.
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Date Created: 04/15/16
Thermodynamics and Thermochemistry Summary Terms and definitions: H (enthalpy) is the change in heat at a constant temperature 1. If delta H is positive heat is taken away from the surroundings and it is considered exothermic 2. I delta H is negative, heat is given/added to the surroundings and I is considered exothermic S (entropy) is the change in randomness or how spontaneous it is 1. If S > 0, then there is an increase in randomness. This is thermodynamically favored 2. If S < 0, then there is a decrease in randomness. This is NOT thermodynamically favored G (Free Energy change) – relates to ideal work from reaction and it CANNOT be measured. 1. If G > 0, then it is nonspontaneous and needs an external driving force 2. If G < 0, then it is spontaneous and does not need an external driving force Standard State: Is a state that is defined when a pure solid, liquid, or gas is at 1 atmosphere pressure and 1M concentration. Laws of thermodynamics: First Law of Thermodynamics: Law of Conservation of Energy. For review purposes, the law of conservation is that: energy cannot be created or destroyed, but only changed from one form into another or transferred from one object to another. Second Law of thermodynamics: Spontaneous processes lead to increase of entropy of the universe Third Law of Thermodynamics: Only a perfect crystal at 0 kelvin has zero entropy Entropy Relationships 1. Gases have higher entropy than liquids, which have a higher entropy than solids, so g>l>s 2. Mixtures > pure substances, except when going down in phase 3. Between substances in the same phase: If there are more atoms and/or the substance is heavier, the greater the entropy is 4. For reactions in the same phase if more molecules are made, the higher the entropy 5. Increase in temperature = increase in entropy, decrease in pressure = increase in entropy Relationship between Entropy, Enthalpy, and Free Energy + + positive at low temp, negative at high temperature + always positive + always negative negative at low temp, positive at high temperature >>1 very negative >1 negative 1 0 <1 positive <<1 very positive Equations: H reaction = [H(pfoducts)] – [H(reactfnts)] H f elements in natural state = 0 S = [S(products)] – [S(reactants)] reaction f f G reaction = [G(pfoducts)] – [G(reactfnts)] G f elements in natural state = 0 For Entropy H = TS(surroundings) S(universe) = S(reaction) + S(surroundings) G = TS(universe) For Delta G: G = H TS (T in K; get ALL quantities in either Joules or Kilojoules) G = RTlnK (R = 8.314; T in K; G in JOULES) (G refers to energy change going from all things in standard state to equilibrium) G = G + RTln Q (G refers to energy change for ANY stage of reaction)
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