1. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA1
Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

2. Applications of First Law of Thermodynamics
Sajjad Ahmed Memon
Senior Scientist
NIMRA

3. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA
Heat can be supplied to a thermodynamic system under the following conditions: Isobaric Process Isochoric Process Isothermal Process Adiabatic Process
Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

4. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA
Isobaric Process
A thermodynamic process in which pressure of the system remains constant during the supply of heat.
Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

5. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA
Consider a cylinder fitted with a frictionless piston. The piston is free to move in the cylinder. An ideal gas is enclosed in the cylinder.
Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

6. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

7. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA
DQ = DU + DW But DW = PDV Thus DQP = DU + PDV As DV = (V2 - V1) DQP = DU + P (V2 - V1)
Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

8. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

9. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA
Isochoric Process
A thermodynamic process in which the volume of the system remains constant during the supply of heat.
Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

10. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA
Consider a cylinder fitted with a frictionless piston. An ideal gas is enclosed in the cylinder. The piston is fixed at a particular position so that the volume of cylinder remains constant during the supply of heat.
Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

11. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

12. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA
Let DQ amount of heat is added to the system. Addition of heat causes the following changes in the system: DQ = DU + DW But DW = PDV Thus DQ = DU + PDV As DV = 0 DQ = DU + P (0) = DU
Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

13. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA
This expression indicates that the heat supplied under isochoric process is consumed in increasing the internal energy of the system but no work is performed.
Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

14. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

15. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA
Isothermal Process
A thermodynamic process in which the temperature of the system remains constant during the supply of heat.
Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

16. Isothermal Compression
Consider a cylinder of non-conducting walls and good heat conducting base. The cylinder is fitted with a frictionless piston. An ideal gas is enclosed in the cylinder. In the first stage pressure on the piston is increased and the cylinder is placed on a cold body. Due to compression, the temperature of the system increases but at the same time DQ amount of heat is removed from the system and the temperature of the system is maintained.
Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

17. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA
DQ = DU + DW Since temperature is constant, therefore, there is no change in internal energy of the system. i.e. DU = 0 As the work is done on the system, therefore, DW is negative DQ = 0 + (-DW) DQ = -DW
Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

18. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA
Isothermal Expansion
In another situation the cylinder is placed over a hot body and the pressure on the system is decreased. Due to expansion, the temperature of the system is decreased but at the same time DQ amount of heat is absorbed from the hot body and the temperature of the system is again maintained.
Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

19. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA
DQ = DU + DW
Since temperature is constant, therefore, there is no change in internal energy of the system. i.e. DU = 0
As the work is done by the system, therefore, DW is positive
DQ = 0 + (DW) DQ = +DW
Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

20. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

21. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA
Adiabatic Process
A thermodynamic process in which there is no heat transfer into or out of the system takes place. In other words DQ = 0.
An adiabatic process is generally obtained by surrounding the entire system with a strongly insulating material or by carrying out the process so quickly that there is no time for a significant heat transfer to take place.
Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

22. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA
DQ = DU + DW Since there is no heat transfer into or out of the system. i.e. DQ = 0. 0 = DU + DW DU = - DW
Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

23. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA
Since DU is the change in internal energy and DW is the work done by the system, therefore the possible outcomes: 1. A system that expands under adiabatic conditions does positive work, so the internal energy decreases. 2. A system that contracts under adiabatic conditions does negative work, so the internal energy increases.
Sajjad Ahmed Memon S.S./ Health Physicist NIMRA

24. Sajjad Ahmed Memon S.S./ Health Physicist NIMRA