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L30-post

# L30-post - N2O4(g Lecture 30 Pressure(atm Pressure of Gases...

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1 Lecture 30 Make It Work: Heat and work Key Idea: Chemical energy can be converted into work required to move objects. Time Pressure (atm) Pressure of Gases over Time N 2 O 4 4 (g) (g) 2 NO NO 2 ( g) 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 P N2O4 P NO2 and K p = 0.15 G o = + 4.73 kJ = RT ln K > 0 Reactant-favored .... So then WHY does product form?! Q initial = 0 ! (no products!) Some product must form! G = G o + RT ln Q = +4730 J/mol + (8.314 J/molK)(298.15 K) ln (0.10) 2 (1.95) = +4.73 J + ( 13.1 kJ) = 8.3 kJ < 0 ! E.g., for small, non-zero Q! As Q to K, G becomes less negative. At equilibrium, G = ? G = G o + RT ln Q 1. At equilibrium, Q = K and G=0. 2. If Q < K, then G < 0 and products form until Q=K . 3. If Q > K, then G > 0 and nothing happens. 4. If Q > K, then G > 0 and reactants form until Q=K. 5. In general, equilibrium should be considered when | G o | is < 100 kJ. For reactions that can reach an equilibrium, which statements are true? ChemQuestion A. 1,2,3 B. 1,2,4,5 C. 1,2,3,5 D. 2,3 E. 1,2,4 CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O (l) H o rxn = 890.36 kJ/mol of CH 4 S o rxn = 242.98 J/K mol of CH 4 G o rxn = 817.90 kJ/mol of CH 4 : Heat given off (changing bonds!) : Some of heat goes into S surr > 0 : Resulting in a less negative G o

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