2300_les05 - II. Energy and the First Law of Thermodynamics...

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1 lesson 5 II. Energy and the First Law of Thermodynamics A. Energy Transfer as Heat Transfer. Energy is Conserved. 1. Energy can cross the boundary of a closed system by only two mechanisms: heat transfer and work transfer. 2. The change in energy of a closed system is equal to the net heat transferred to the system minus the net work performed by the system. ,, sys in net out net EQ W ∆= Closed system Net work out, W out,net = W out -W in Net heat in, Q in,net = Q in -Q out (2-34), p. 73; (4-17), p 174 total system surroundings EE E 0 ∆∆ =+ = system surroundings =− lesson 5 II. Energy and the First Law of Thermodynamics B. Heat transfer 1. Heat is energy transferred across the boundary of the system due to a difference in temperature between the system and the surroundings . a. The heat flux, , is the rate of heat transfer per unit area of surface. The units are W/m 2 or kW/m 2 or Btu/(ft 2 h) b. The heat transfer rate (kW) is calculated from the heat flux as = A dA q Q ± ± A is the area over which heat transfer is occurring.
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This note was uploaded on 09/04/2009 for the course CHEM 2300 taught by Professor Thermo during the Summer '08 term at University of Utah.

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2300_les05 - II. Energy and the First Law of Thermodynamics...

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