LECTURE4

# LECTURE4 - Last Time State and path dependent functions Work Work done during reactions Heats of reactions under constant volume and constant

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Last Time State and path dependent functions Work Work done during reactions Heats of reactions under constant volume and constant pressure The state function Enthalpy, H Heats of formation Heats of reaction Hess’ Law A C B D ? H (AC) H (DB) H (CD) Recall: H is a state function: path independent! A C H (AC) C D H (CD) D B H (DB) A B H (AB) If a process occurs in stages or steps (even hypothetically), the enthalpy change for the overall process is the sum of the enthalpy changes for the individual steps.

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Hess’s Law ½N 2 (g) + O 2 (g) NO 2 (g) H° = ½N 2 (g) + ½O 2 (g) NO(g) H° = +90.25 kJ NO(g) + ½O 2 (g) NO 2 (g) H° = -57.07 kJ H is extensive: H = U + PV PCl 3 (l) + Cl 2 (g) PCl 5 (l); Hº = PCl 5 (l) PCl 3 (l) + Cl 2 (g); H o = +123.8 kJ 4PCl 5 (l) 4PCl 3 (l) + 4Cl 2 (g); H o = Can multiply: Can reverse:
Calculate f of PCl 3 Given: I: P 4 (s) + 10 Cl

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## This note was uploaded on 07/09/2011 for the course CHE 2B 2B taught by Professor Tobyallen during the Spring '11 term at UC Davis.

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LECTURE4 - Last Time State and path dependent functions Work Work done during reactions Heats of reactions under constant volume and constant

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