Work done on system, W. Work is computed by original definition: the component of force moving through a distance. Examples in internal combustion engine.
Heat absorbed by system, Q. Examples in internal combustion engine.
First Law. Energy of system U -- the sum of work done on system W and heat absorbed by system Q -- is conserved, that is, U = W + Q is conserved.
Heat QH > 0 added at constant TH. Piston moves out: WH < 0 . (1→2)
|Expanding gas pushes piston as TH drops to TL. (2→3) [adiabatic process]|
|QL < 0 extracted at TL. Piston moves in: WL > 0. (3→4)|
|Contracting gas drags piston as TL rises to TH.(4→1) [adiabatic process]|
Work done by system W =WL-WH ⇒ QH=W+QL.
Reviewing steps in which we ignore work change during heating and cooling and heat changes during work in or work out. In other words, we assume energy is conserved in actual engine.
The efficiency is the work done (W) compared to the total energy input QH.
|=||(QH- QL)/QH||(Thermo 1st law; conservation of energy|
|=||1 - TL/TH||Q ∝T (coming attraction)|
When a material changes phase -- e.g., ice to water or water to steam -- extra energy is required to convert one 1 kg from one phase into another. These are called Latent Heat of Fusion or Latent Heat of Evaporation, respectively.
|Temp C||kJ/kg||Temp C||kJ/kg|
If added 1 kg of ice at 0 C to 10 kg of water at 10 C, what is temperature of final mixture?
Ice will melt and form 11 kg of water. The specific heat of water is
or T = 10 - 345/11./4.2 = 2.6 C.