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Unformatted text preview: Chapter 7 Thermodynamic: The First Law Thermodynamics Study of transforma:on of energy from one form to another Systems & surroundings System is part of universe under study Surrounding is rest of universe Open system: ﬂow of [email protected] and energy [email protected] Closed system: ﬂow of [email protected] prevented but energy [email protected] Isolated system: ﬂow of [email protected] and energy prevented Work and Energy Work is achieving mo:on against opposing force w=F×d
Energy is capacity of system to do work Internal energy (U): total energy content of system €
Measure change in internal energy (ΔU) When system does work, loses poten:al energy & internal energy work = ΔU € Expansion Work Work which results when gas compressed or expanded under external pressure Assuming external pressure constant Pex = F
A F = Pex A
€
€3
1Pa⋅ m = 1J 1L⋅ atm = 101.325 J
€ € w = F × d = Pex A × d w = −Pex × ΔV € € Expansion Work A cylinder conﬁnes 2.00 L of gas under a pressure of 1.00 atm. The external pressure is also 1.00 atm. The gas is heated slowly with the piston sliding freely to maintain the pressure of the gas close to 1.00 atm. Suppose the hea:ng con:nues un:l a ﬁnal volume of 3.50 L is reached. Calculated the work done on the gas. Expansion Work Work which results when gas compressed or expanded under external pressure Work done against changing external pressure Reversible expansion: expansion against external pressure that changes so that it matches the pressure of the system Irreversible expansion: expansion against external pressure that diﬀers by ﬁnite amount from pressure of system dw = −Pex dV
dw = −P ⋅ dV
nRT
dw = −
dV
V €
€
w=
€
€ ∫ Vf
Vi Vf dw = −nRT ∫V Vf
w = −nRT ln
Vi i dV
V Expansion Work A piston contains 0.200 mol nitrogen in 2.00 L at 25oC. Calculate the work done when the gas expand to 3.00 L against a constant pressure of 1.00 atm. Calculate the work done when the gas expands reversibly and isothermally to 3.00 L. ...
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This note was uploaded on 01/25/2012 for the course CHEM 14BL B taught by Professor Sakira during the Fall '11 term at UC Irvine.
 Fall '11
 sakira

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