16_LectureWeb - Learning Objectives You should 1 know that...

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Learning Objectives 3/11/08 You should: 1. know that in spontaneous processes D S univ > 0 and understand that the Gibbs free energy change ( D G ) provides an alternate way to express the criterion for spontaneity entirely in terms of properties of the system. 2. know the Gibbs free-energy criterion for spontaneity ( D G < 0). 3. understand that a negative enthalpy change for the system ( D H ) will cause an increase in the entropy of the surroundings through the transfer of heat. 4. be able to apply the Gibbs-Helmholtz equation to predict the temperature dependence of D G °. 5. understand the difference between D G ° and D G. 6. be prepared to apply the relationship between D G ° and D G. 7. be able to calculate K if given D G ° and vice versa. 8. know how to use the Van’t Hoff equation to determine the temperature dependence of K . Recall that in a spontaneous process D S universe =D S sys +D S surr > 0 In order for the entropy of the surroundings to change, heat must be transferred between the system and the surroundings. If heat is transferred from the system to the surroundings at constant pressure, D S surr =- D H sys ÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅ T Consequently, D S sys - D H sys ÅÅÅÅÅÅÅÅÅÅÅÅÅÅÅ T > 0 H multiply both sides of equation by - T L - T D S sys +D H sys < 0 D H sys - T D S sys =D G sys < 0 For all spontaneous processes, D G < 0. Ë This requires that D H < 0 (enthalpy driven) and/or D S > 0 (entropy driven). *** The advantage of expressing the criterion for spontaneity in terms of G rather than D S is that D G is a function only of what is happening in the system. *** 2 Example: Relationship Between D G , D H , and D S Consider the spontaneous reaction for forming water from hydrogen and oxygen
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16_LectureWeb - Learning Objectives You should 1 know that...

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