Energy Equation 2nd Law of Thermodynamics Energy cannot be created or destroyed. (see Conservation of Mass for exception) It can, however, change from one form to another; transfer from one system to another. Energy conservation is a Postulate

Closed System In a closed system no mass enters or leaves the system. However, energy can leave as –Work [W] (organized motion) –Heat [Q] (random motion)

1st Law for Closed System dE CM =  Q +  W Work done by system (out) +ve Heat supplied to system (in) +ve d - exact differential (state variable)  - not e. d. (path dependant) Same per mass, per mole.

Other Forms of 1st Law In rate form: In integral form:

Applications of 1st Law Fixed volume: pdV = 0 only internal energy, E = U

Applications of 1st Law Constant pressure, slow moving piston No kinetic energy, no potential energy

Application of 1st Law Piston with friction: Without (a): With (b): 1st Law still:

Assume:ideal gas, same initial/final volume For either a) or b): Then: But: Application of 1st Law

Less energy (heat transfer) required for same expansion process without friction. Show for yourselves: if p a same as p b the gas would expand less since some of the work used to overcome friction

Application of 1st Law Heat from saturated liquid to saturated vapor at constant p: Q 12 =  H 12 = m(h g - h f ) = mh fg h fg - latent heat of vaporization Similarly: latent heat of fusion latent heat of sublimation

1st Law with Shaft Work

Cycles A repeated thermodynamic cycle where the initial state equals the final state. denotes integration over a cycle By definition:

Cycles First law: Net work out = net heat in: Cycle efficiency: