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Unformatted text preview: L ECTURE 21. T HERMODYNAMICS —L ET ’ S G ET Q UANTITATIVE Today we will examine the quantitative side of thermodynamics, while actually coming up with numerical values for Δ H, Δ S, etc. Up to this point we have been more concerned with the signs of thermo data and what they mean. These are summarized below and should be as much a part of you as your own name: (-) Exothermic, Heat Released, Hot Δ H (+) Endothermic, Heat Absorbed, Cold (-) Spontaneous Δ G (+) Non Spontaneous (+) Disordered Δ S (-) Ordered (-) A Bomb, Work Done on Surroundings w (+) “Arming a Bomb” Work Done on System But now we will be adding numbers: C 3 H 8 + 5O 2 3C0 2 + 4H 2 O Is NOT just Δ G = (-) It IS Δ G = -2070kJ which means it is really spontaneous. (Still, while we learn to do these calculations, don’t forget the importance of simply looking at a reaction and being able to assign the signs! It is knowing the signs that proves you understand thermo-- anyone can put numbers in a calculator but since half the questions I put on tests don’t require a calculator…..) How to complete the Thermodynamic Reaction Worksheet Predict the values for Δ H, Δ n gas, w, Δ S, and Δ G. At the least provide a sign, but if you can offer a guess of the magnitude without using a calculator, that is even better. First the signs. Can you explain how you know them? Reaction Δ H Δ n gas w Δ S Δ G CH 4(g) + O 2(g) CO 2(g) + 2H 2 O (g) (-) 0 0 (-) (-) 2H 2(g) + O 2(g) 2H 2 O (g) (-) (-) + (-) (-) And now the calculations....
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This note was uploaded on 05/21/2008 for the course CH 301 taught by Professor Fakhreddine/lyon during the Spring '07 term at University of Texas.
- Spring '07