lec2 - Last Time First Law of Thermodynamics U = q + w heat...

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1 Last Time • First Law of Thermodynamics Δ U = q + w – heat emitted q heat + heat absorbed – work delivered w work + work accepted • Know q and w calculate Δ U Heat q • Unit of heat: calorie – 1 cal = amount of energy required to heat 1 g of H 2 O by 1 ° C • Standard S.I. Unit: Joule – 1 cal = 4.184 J • Different materials heat differently Basis for Comparison • Heat capacity = heat supplied / temp. rise c p = • Officially: heat required to raise T by 1 ° C • Units: J / ° C or J / K • Poor measure: Extensive property q Δ T

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2 Better Estimates • Molar heat Capacity: C p C p = • Specific heat Capacity: C sp C sp = • Both C p and C sp are intensive properties q n Δ T q m Δ T J mol ° C J g ° C Uses of C p and C sp • C p and C sp are tabulated – calculate heat q = nC p Δ T = mC sp Δ T J = mol (J/mol ° C) ° C = g (J/g ° C) ° C – determine heat flow • Typical values – C sp (H 2 O) = 4.184 J/g ° C – C sp (C 6 H 6 ) = 1.05 J/g
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This note was uploaded on 03/18/2012 for the course CHEM 2B taught by Professor Clemens during the Winter '08 term at UC Davis.

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lec2 - Last Time First Law of Thermodynamics U = q + w heat...

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