Thermodynamic Processes. Illustrate how the 1 st law of thermodynamics is a statement of energy conservation Calculate heat, work, and the change in internal energy by applying the 1 st law of thermo Apply 1 st law of thermo to cyclic processes.
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Illustrate how the 1st law of thermodynamics is a statement of energy conservation
Calculate heat, work, and the change in internal energy by applying the 1st law of thermo
Apply 1st law of thermo to cyclic processes
The PE depends only on the car’s elevation.
The new ME bar should equal KE + PE in each case. Thus, it will get shorter from (b) to (e) as the U bar gets taller by the same amount.
+ for heat added; - for heat lost
+ work done by the system; - work on system
ΔU = Uf- Ui
ISOBARIC (constant P) ISOVOLUMETRIC
Delta P=0 delta V=0
W=Fd=P(ad)=P delta V W=0, Q=deltaU
Q=delta U+W=delta U+P delta V
Unet = 0 + Qnet = Wnet
Qnet = Wnet
Where Qh > Qc
The colder you want the inside of a refrigerator to be, the greater the net energy transferred as heat (Qh – Qc) must be.
*A refrigerator performs work to create a temperature difference between its closed interior and its environment.
*Transfers energy from a body at low temperature to one at a high temperature.
*Uses work performed by an
electric motor to compress
In each of the 4
steps of a
cycle, energy is
transferred to or
by heat or by work.
Cyclic Process Frige
1: Electrically-run compressor does work on the Freon gas, increasing the pressure of the gas.
High Pressure and High Temperature
2: High Pressure Freon Gas released into external heat enters exchange coil on the outside of the refrigerator
3: Heat flows from High Temperature gas to the lower-temperature air of the room surrounding the coil. This heat loss causes the Freon to condense to a liquid releasing heat to outside of the refrigerator. (space behind the frige)
4: As Freon passes through the expansion valve it expands and evaporates
now at low pressure and low temperature
5: Evaporating Freon absorbs heat from inside the refrigerator. This causes the refrigerator to cool as its heat is absorbed by the evaporating Freon in the internal coils. Thus, temperature inside refrigerator is reduced
6: When all Freon changes to gas, the CYLCE REPEATS