1. PROPERTITES OF GASES (2)
MOUNTAIN TOP UNIVERSITY
CHM 101
PROPERTITES OF GASES (2)
Dr. (Mrs.) Ndukwe, Nelly Acha
          PROPERTITES OF GASES (2) by Dr. (Mrs.) Ndukwe, Nelly Acha is licensed under a Creative Commons Attribution-Non Commercial 4.0 International License

2. Properties of Gases Cont.
A gas has no definite shape or volume of its own. It acquires the shape of the container.
Weakest Intermolecular attraction occurs in gases while intermolecular separation is the largest, causing gas molecules to move very fast and the gas expands to fill all the space available.
A gas has no surface of its own as molecules can escape from an open container.

3. Properties of Gases
A gas can diffuse into another gas as molecules move very fast leading to large increase in the speed of diffusion
A gas on cooling changes into liquid state as cooling reduces intermolecular separation and increase intermolecular force of attraction
A gas can flow in all directions and thus requires a closed vessel from all sides
A gas is not rigid and can easily be compressed due to increase in intermolecular separation in gaseous state

4. Ideal Gas versus Real Gas
An ideal gas is a hypothetical or imaginary gas that is assumed to have no intermolecular forces of attraction. Its molecules are also assumed to undergo elastic collisions with each other and with the walls of the container
A real gas that does not obey these assumptions, but at high temperatures and low pressures where a real gas molecules are far apart from each other it can behave like an ideal gas.
In the ideal gas the particles have zero volume while in a real gas the molecules have a small but not zero volume
In ideal gas collisions and no loss in total kinetic energy while in real gas collisions are inelastic and when gas particles collide they will lose energy

5. Boyle's Law
At constant temperature, the volume of a gas is inversely proportional to the pressure.

6. The Five Basic Tenets of The Kinetic Theory of Gases
A gas is composed of molecules that are separated by average distances that are much greater than the sizes of the molecules themselves. Hence, the volume occupied by the molecules of the gas is negligible compared to the volume of the gas itself.
The molecules of an ideal gas exert no attractive forces on each other, or on the walls of the container
The molecules are in constant random motion, and as material bodies, they obey Newton's laws of motion. This means that the molecules move in straight lines until they collide with each other or with the walls of the container.

7. The Five Basic Tenets of The Kinetic Theory of Gases
2 Collisions are perfectly elastic; when two molecules collide, they change their directions and kinetic energies, but the total kinetic energy is conserved. Collisions are not “sticky".
3 The average kinetic energy of the gas molecules is directly proportional to the absolute temperature. Meaning that the velocities and kinetic energies of individual molecules will have wide range of values as temperature changes.
Some gas molecules will even have zero velocity at a given temperature. And all molecular motion would cease if the temperature were reduced to absolute zero.

8. Calculations on Properties of Gases
Example 1: A sample of gas has a volume of 6.20 L at 20°C and atm pressure. What is its volume at the same temperature and at a pressure of 1.11 atm?
V1/T1 = V2/T2
Solution : V1= 6.20 L, P1= atm, V2= ?, P2 = 1.11 atm. Check the pressure unit. If they are different
Substitute the Boyle's Law Equation:
V2= V1 x P1/P2 = 6.20 L x atm/1.11 atm
= 5.47 L Ans

9. Charles' Law
At constant pressure, the volume of a gas sample is directly proportional to the temperature in degrees Kelvin

10. Calculations on Properties of Gases
Example 2: The volume of a gas sample is 746 mL at 20° C. What is its volume at body temperature (37°C)? Assume the pressure remains constant
Charles' Law = V1/T1 = V2/T2
Solution : V1= 746 mL, T1= 20° C, V2= ?, T2= 37°C
T1 = = 293 K, T2 = =310 K.
To calculate the new volume: V2= V1 T2/T1 = 746mL X 310 K/293 K = 789 mL Ans

11. The Combined Gas Equation
P1V1/T1 = P2V2/T2
Example 3: A gas sample occupies a volme of 2.5 L at 10°C and 0.95 atm. What is its volume at 25°C and 0.75 atm?
Solution : V1= 2.5 L, T1= 10°C = 283 K, P1= atm, T2 = 25°C + 273= 298K, V2 = ?
0.95 atm x 2.5L/283 K x 0.75 atm x V2/ 298 K
V2 = 0.95 atm x 2.5L x 298 K /283 K x 0.75 atm
V2 = 3.3 L Ans

12. Calculation on Ideal Gas Equation
PV nRT
Example 4: What volume is occupied by 5.50 g of carbon dioxide at 25°C and 742 torr?
Solution : Identify the variables in the equation, and convert the units to match those of the gas constant. We will use the gas constant L-atm/mol-K. This value establishes the units of volume (L), of pressure (atm), of moles, and temperature (K) to be used in solving the problem.

13. Calculation on Ideal Gas Equation
PV = nRT
P= 742 torr x 1 atm / 760 torr = atm
V = ? L, n = 5.50g x 1 mol / 44.0 g = mol
R = L atm/mol –k, T = = 298 K.
V= nRT /P,
V = mol x ( L atm / mol-k)(298 K) / atm
V = 3.13 L Ans

14. Several Values of the Gas constant R
Units
0.0821
1-atm/mol-K
8.31 X 103
L-Pa/mol-K
62.4
L-torr/mol-K
8.31
m3-Pa/mol-K
PROPERTITES OF GASES (2) by Dr. (Mrs.) Ndukwe, Nelly Acha is licensed under a Creative Commons Attribution-Non Commercial 4.0 International License