Meeting%2019%20F%202010

Meeting%2019%20F%202010 - Meeting 19 Last time we saw how...

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1 Meeting 19 Last time we saw how to measure “heats” of reaction, Δ H rxn using calorimetry. For some reactions it is impossible to use this technique. Example: 2C(Gr)) + O 2 (g) → 2CO(g); Δ H = ? The reaction cannot be stopped at CO, and CO 2 (g) forms. What to do? Calculate Δ H from reactions whose Δ H rxn s are known . Use Hess’s Law of Constant Heat Summation: The heat of a reaction is constant, whether the reaction is carried out directly or via a number of steps . ΔH overall = Σ ΔH’s of individual reactions Reverse an equation, change the sign of Δ H.\ Multiply an equation’s coefficients, multiply Δ H by the same coefficient for that reaction
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2 ( Example: Calculate Δ H rxn for 2C(Gr) + O 2 (g) → 2CO(g) Use enthalpy diagram ΔH(a) + Δ H(b ) = Δ H(c) ; Δ H(a) = -110.5 k J. A more complex example Calculate the enthalpy change for reaction a) given the data in equations (b), (c), and (d) a) 2C(gr) + 2H 2 (g) → C 2 H 4 (g) Δ H = ? b) C(gr) + O 2 (g)→ CO 2 (g) Δ H = –393.5 kJ c) C 2 H 4 (g) + 3 O 2 (g)→2CO 2 (g + 2H 2 O(l) Δ H = –1410.9 kJ d) H 2 (g) + ½ O 2 (g) →H 2 O(l) Δ H = –285.8 kJ Manipulate b), c) & d) to get a)
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3 2 b – C + 2 D gives eq.a: of all the other factors cancel.
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This note was uploaded on 03/08/2011 for the course CHEM 161 taught by Professor Vacillian during the Fall '08 term at Rutgers.

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Meeting%2019%20F%202010 - Meeting 19 Last time we saw how...

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