1. Physical Chemistry (TKK-2446)
16/17 Semester 2
Physical Chemistry (TKK-2446)
Instructor: Rama Oktavian
Office Hr.: M. 10 – 12, T. 10 – 12, W. 09 – 10, F.10 – 15

2. Outlines 1. Review 2. Molar mass of gas
3. Molar mass of volatile component
4. Gas mixture

3. Review
Learning check
A sealed flask with a capacity of 1 dm3 contains 5 g of ethane. The flask is so weak that it will burst if the pressure exceeds 1 MPa. At what temperature will the pressure of the gas reach the bursting pressure ?

4. Review
Learning check
A perfect gas undergoes isothermal compression, which reduces its
volume by 1.80 dm3. The final pressure and volume of the gas are 1.97 bar and 2.14 dm3, respectively. Calculate the original pressure of the gas in (a) bar,
(b) Torr

5. Review
Learning check
A large cylinder for storing compressed gases has a volume of about m3. If the gas is stored under a pressure of 15 MPa at 300 K, how many moles of gas are contained in the cylinder ?
What would be the mass of oxygen in such a cylinder ?

6. Review
Learning check
A manometer consists of a U-shaped tube containing a liquid. One side
is connected to the apparatus and the other is open to the atmosphere. The
pressure inside the apparatus is then determined from the difference in
heights of the liquid. Suppose the liquid is water, the external pressure is
770 Torr, and the open side is 10.0 cm lower than the side connected to the
apparatus. What is the pressure in the apparatus? (The density of water at
25°C is g cm−3.)

7. Molar mass of ideal gas Determination of molar mass for ideal gas
Ideal gas equation
Intensive properties and measurable

8. Molar mass of ideal gas Determination of molar mass for ideal gas
Gas density
Density is higher
1. for gases with a higher molar mass Gases
2. at higher pressures
3. at lower temperatures

9. Molar mass of ideal gas Determination of molar mass for ideal gas
Example
if chemical analysis of a gas yields an empirical formula (CH 2 )n, then the molar mass must be some multiple of 14 g/mol ; the possibilities are 28, 42, 56, 70, and so on. If a molar mass determination using Eq. (2. 20) yields a value of 54 g/mol, then we may conclude that n = 4 and that the material is one of the butenes.

10. Molar mass of ideal gas Determination of molar mass for ideal gas
Problem : Calculation of Molecular Weight of a
Natural Gas - Methane
A sample of natural gas is collected at 25.0 C in a ml
flask. If the sample had a mass of g at a pressure of torr,
what is the molecular weight of the gas?
Use the ideal gas law to calculate n, then calculate the molar mass.

11. Molar mass of ideal gas Determination of molar mass for ideal gas
Problem
At 100°C and 1.60 kPa, the mass density of phosphorus vapour is
kg m−3. What is the molecular formula of phosphorus under these
conditions?

12. Molar mass of ideal gas Determination of molar mass for ideal gas
Problem
A series of measurements are made in order to determine the molar mass of an unknown gas. First, a large flask is evacuated and found to weigh g. It is then filled with the gas to a pressure of 735 torr at 31°C and reweighed; its mass is now g. Finally, the flask is filled with water at 31°C and found to weigh g. (The density of the water at this temperature is g/mL.) Assuming that the ideal-gas equation applies, calculate the molar mass of the unknown gas.

13. Gas mixture
Air is an example of an ideal gas mixture and has the following approximate composition.
Component % by Volume N O
Argon
CO2 + trace elements

14. Gas mixture Properties of gas mixture
k gases
T = Tm V = Vm
P = Pm m = mm
The total mass of the mixture mm and the total moles of mixture Nm are defined as

15. Gas mixture Properties of gas mixture Volume concentration
Unit : mol/m3
Volume concentration  molarity

16. Gas mixture Properties of gas mixture
The composition of a gas mixture is described by specifying either the mass fraction mfi or the mole fraction yi of each component i.
Note that

17. Dalton’s law Ideal gas law for gas mixture
We define the partial pressure of each gas in the mixture as the pressure the gas would exert if it were alone in the container of volume V at temperature T

18. Dalton’s law
Partial pressure
Dalton’s law

19. Dalton’s law Dalton’s Law of Partial Pressures indicates that
pressure depends on the total number of gas particles, not on the types of particles.
the total pressure exerted by gases in a mixture is the sum of the partial pressures of those gases.
PT = P1 + P2 + P

20. Dalton’s law

21. Dalton’s law
Partial pressures are simply related to the mole fractions of the gases in the mixture

22. Dalton’s law
Partial pressures are simply related to the mole fractions of the gases in the mixture

23. Dalton’s law Learning check
If I place 3 moles of N2 and 4 moles of O2 in a 35 L container at a temperature of 25°C, what will the pressure of the resulting mixture of gases be?
What’s the partial pressure of carbon dioxide in a container that holds 5
moles of carbon dioxide, 3 moles of nitrogen, and 1 mole of hydrogen and
has a total pressure of 1.05 atm?

24. Dalton’s law Learning check
A vessel of volume 22.4 dm3contains 1.5 mol H2and 2.5 mol N2 at
K. Calculate (a) the mole fractions of each component, (b) their partial pressures, and (c) their total pressure

25. Dalton’s law Dalton’s law application in atmosphere
This explains why people usually difficult to breathe in high altitude place even the concentration of oxygen is same (21%)
The transfer of oxygen molecules from the lungs to the bloodstream is dependent on a pressure gradient.

26. Exercise and learning check
Problems
Ch. 1 Atkin’s Physical chemistry 8th ed. Numerical problems no:
1.4
1.5
1.6
Take-home assignment – Theoretical problem 1.24
Chapter 2 Castellan Physical chemistry 3rd ed. Problems no:
2.9
2.13

27. Thank You !