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

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

Review Learning check A sealed flask with a capacity of 1 dm 3 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 ?

Review Learning check A perfect gas undergoes isothermal compression, which reduces its volume by 1.80 dm 3. The final pressure and volume of the gas are 1.97 bar and 2.14 dm 3, respectively. Calculate the original pressure of the gas in (a) bar, (b) Torr

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 ?

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.)

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

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

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.

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.

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?

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.

Gas mixture Air is an example of an ideal gas mixture and has the following approximate composition. Component % by Volume N O Argon 0.92 CO2 + trace elements 0.03

Gas mixture Properties of gas mixture k gases T = T m V = V m P = P m m = m m The total mass of the mixture m m and the total moles of mixture N m are defined as

Gas mixture Properties of gas mixture Volume concentration Unit : mol/m 3 Volume concentration  molarity

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

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

Dalton’s law Partial pressure 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. P T = P 1 + P 2 + P

Dalton’s law

Partial pressures are simply related to the mole fractions of the gases in the mixture

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

Dalton’s law Learning check If I place 3 moles of N 2 and 4 moles of O 2 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?

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

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.

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