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

2. Outlines 1. Change in energy 2. Change in state at constant volume
3. Change in state at constant pressure
4. Adiabatic change state
(Process calculation in ideal gas)

3. Change in energy Energy is an extensive state property of the system
Energy per mole is an intensive state property of the system
Energy is conserved in all transformations
First law thermodynamic
dU = dQ + dW
dU of the system depends only on the initial and final states
Q and W depends on path

4. Change in energy First law thermodynamic dU = dQ + dW
dU of the system depends only on the initial and final states. Define U = U(T,V)
Substituting dU from the first law thermodynamic

5. Change in energy
First law thermodynamic

6. Change in energy First law thermodynamic
This is the general first-law equation for a mechanically reversible, closed-system process

7. Change in energy
Example of energy change – state and path function

8. Change in state at constant volume
First law thermodynamic
Change state at constant volume

9. Change in state at constant volume
New properties – heat capacity
Heat capacity at constant volume

10. Change in state at constant volume
Heat calculation at constant volume
If Cv constant

11. Change in state at constant volume
Heat calculation at constant volume
Valid for constant volume process
Heat calculation at constant volume process

12. Change in state at constant pressure
In laboratory practice most changes in state are carried out under a constant atmospheric pressure

13. Change in state at constant pressure
Recall first law thermodynamics mathematical formulation
Integrating this equation at constant pressure, we obtain

14. Change in state at constant pressure
Rearranging this equation

15. Change in state at constant pressure
Introducing new extensive state property of system
Enthalpy
Valid for constant-pressure process

16. Change in state at constant pressure
Heat calculation at constant pressure process
constant pressure process

17. Change in state at constant pressure
Heat calculation at constant pressure process
Heat capacity at constant pressure process
If Cp is constant
Valid for constant pressure process

18. Implied property relation for ideal gas
Relation between Cv and Cp

19. Adiabatic change
Adiabatic – no heat flow
the first law statement is

20. Adiabatic change
Adiabatic change state in ideal gas
For ideal gas

21. Adiabatic change
Integrating this equation from initial state (T1, V1) into final state (T2, V2), we have
If Cv is independent to temperature (T)

22. Adiabatic change
For ideal gas we have relationship

23. Adiabatic change
PVT relationship for adiabatic change state in gas ideal

24. Adiabatic change
Adiabatic change PV-graph

25. Learning check Check and Re-do example 7.3 from Castellan
An ideal gas, Cv = 5/2 R, is expanded adiabatically against a constant pressure of 1 atm until it doubles in volume. If the initial temperature is 25 °C, and the initial pressure is 5 atm, calculate T2 ; then calculate Q, W, ΔU, and ΔH per mole of
gas for the transformation.

26. Assignment
Open your textbook (Castellan) and do these following problem:
Problem 7.1, 7.4, 7.10, 7.15, 7.17
The constant-pressure heat capacity of a sample of a perfect gas was found to vary with temperature according to the expression Cp /(J K−1) = (T/K). Calculate q, w, ΔU, and ΔH when the temperature is raised from 0°C to 100°C (a) at constant pressure, (b) at constant volume.

27. Process in ideal gas
Isothermal Process (constant temperature) for closed system process
Governing equation

28. Process in ideal gas
Isobaric Process (constant pressure) for closed system process

29. Process in ideal gas
Isochoric Process (constant volume) for closed system process

30. Process in ideal gas
Example

31. Thank You !