Work Work is any energy exchange that is not heat meter Work is any interaction that could have as the sole effect the raising of a weight k g Work force. distance
Work • Work is any energy exchange that is not heat. • Work is any interaction that could have as the sole effect the raising of a weight. • Work = force · distance 1 kg 1 meter
State Function vs. Path Function A state function is a state B property of a system that depends only on Its current state and not on how that state was reached path I A path function state A depends on how the state was reached
State Function vs. Path Function • A state function is a property of a system that depends only on its current state and not on how that state was reached. • A path function depends on how the state was reached. state A state B path 1 path 2
The first law ·dU=dw+dq state B defines the internal energy change of a system The internal energy is a function of state Corollary: Energy is state A conserved in an isolated system
The First Law • dU = dw + dq defines the internal energy change of a system. • The internal energy is a function of state. • Corollary: Energy is conserved in an isolated system. state A state B w q w q
Work of expansion/Compression ex Per external pressure ·A= piston area dz= displacement Z ·d=-Adz= volume change for the gas ·ah=Fdz gas ex A
Work of Expansion/Compression gas dz pex • pex = external pressure • A = piston area • dz = displacement • dV = - A dz = volume change for the gas • dw = F dz dw = - pex dV A
Reversible Changes a reversible change is one that can be reversed by an infinitesimal modification of a variable In a reversible expansion or compression, Pex pgas
Reversible Changes • A reversible change is one that can be reversed by an infinitesimal modification of a variable. • In a reversible expansion or compression, pex = pgas pex pgas