1. Physical Chemistry I (TKK-2246)
13/14 Semester 2
Physical Chemistry I (TKK-2246)
Instructor: Rama Oktavian
Office Hr.: M.13-15, Tu , W , Th , F

2. Outlines 1. Expansion work 2. Multistage expansion
3. Work of expansion
4. Maximum and minimum work

3. Review
Suggest a system, boundary, and surroundings for 10 moles of propane gas in a rigid metal cylinder
Suggest a system, boundary, and surroundings for 500 mL of water in an open beaker.

4. Review
Describe three commonplace examples of how work is done on or by a system
A plumber of mass 65 kg carries a toolbox of mass 15 kg to a fifth floor walk-up apartment 15 m above ground level. Calculate the work required for this process
Describe the internal energy change and work performed when a spring is compressed or expanded.

5. 1st law of thermodynamics
Mathematical statement for The 1st Law of Thermodyamics
ΔU = q + w
in which w > 0 or q > 0 if energy is transferred to the system as work or heat and w < 0 or q < 0 if energy is lost from the system as work or heat

6. Heat, work, and energy
Work (W) - any quantity that flows across the boundary of a system during a change in its state
Ex:
- gas that pushes out a piston and raises a weight
- A chemical reaction that drives an electric current
through a resistance also does work

7. Expansion work the work arising from a change in volume Ex:
- the work done by a gas as it expands and drives back the
atmosphere
- The term ‘expansion work’ also includes work associated with negative
changes of volume, that is, compression

8. Expansion work General expression of expansion work
the work required to move an object a distance dz against an opposing force of magnitude F is

9. Expansion work General expression of expansion work
the work arising from a change in volume

10. Expansion work General expression of expansion work
Integrating equation from initial to final volume

11. Expansion work Reversible expansion
In a reversible process the system is at equilibrium at every stage of the process
Reversibility during pressure changes ensures that
the pressure on the inside of the container is always equal to the pressure
exerted on the outside of the container

12. Expansion work Reversible expansion When we set pex = p
the pressure on the inside of the container is always equal to the pressure
exerted on the outside of the container
The total work of reversible expansion is therefore

13. Expansion work Isothermal reversible expansion
Consider the isothermal, reversible expansion of an ideal gas
the work of reversible isothermal expansion of a perfect gas from Vi to Vf at a temperature T is

14. Expansion work
Isothermal reversible expansion

15. Expansion work
Isothermal reversible expansion

16. Multistage expansion work
Multistage irreversible isothermal expansion and compression
where n is number of stage

17. Maximum and minimum work
Reversible processes actually do not occur
in nature
They are simply idealization of actual
Processes
Easy to analyze
Serve as idealized model

18. Maximum and minimum work
when Reversible processes are approximated instead of the Actual ones
Work-producing devices such as car engine and gas or steam turbine deliver the maximum work, and
Work-consuming devices such as compressors, fan, and pumps
Consume the minimum work.

19. Exercise
A chemical reaction takes place in a container of cross-sectional area
50.0 cm2. As a result of the reaction, a piston is pushed out through 15 cm
against an external pressure of 121 kPa. Calculate the work done by the
system

20. Exercise Isothermal compression
A sample consisting of 2.00 mol He is expanded isothermally at 22°C
from 22.8 dm3 to 31.7 dm3 (a) reversibly, (b) against a constant external
pressure equal to the final pressure of the gas. For the two processes calculate w

21. Exercise Isothermal compression, maximum and minimum work
Three moles of an ideal gas are compressed isothermally from 60 L to 20 L using a constant pressure of 5 atm. Calculate W.
If that gas is compressed reversibly, calculate W

22. Thank You !