lecture38 - V. The first low of Thermodynamics...

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V. The first low of Thermodynamics (conservation of energy) dU = dQ - dW 1. Macro- a micro- parameters Equation of state for monatomic ideal gas: Thermodynamic equilibrium 2. Internal energy (kinetic plus potential energy of particles) dU = dQ + dW ext dW ext = -dW dW = P dV dQ = T dS dU = dQ - dW = T dS - P dV RT m PV Δ U = Δ Q - Δ W
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3. Work V P V 1 V 2 1 2 Δ W = P(V 2 -V 1 )>0 V P V 2 V 1 2 1 Δ W = P(V 2 -V 1 )<0 Δ W 12 = 0 Δ W 23 > 0 Δ W 34 > 0 Δ W 42 < 0 Work is path dependent Heat is path dependent Internal energy is path independent V P V 1 V 2 1 2 Δ W V P V 1 V 2 1 2 3 4 Δ W PdV PAdx Fdx dW 2 1 ) ( V V dV V P W PdV dW
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Example1: A quantity of air is taken from state a to state b along a path that is a straight line in the PV-diagram, where V a =0.070 m 3 , V b =0.110 m 3 , P a =1.00*10 5 Pa, P b =1.40*10 5 Pa. Assume that the gas is ideal. a) What is the work, W, done by the gas in this process? V P a b V a V b W = ½ (P a + P b )(V b -V a ) W = ½ (1.00 + 1.40)* 10 5 Pa*(0.1100 - 0.0700 ) m 3 W = 4.8* 10 3 J b) What happen with temperature and internal energy of this gas? For ideal gas
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lecture38 - V. The first low of Thermodynamics...

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