1. Gas Laws

2. Properties of Gases
Gases are very different from solids and liquids which have definite volumes.
Gases expand to fill any space made available to them.
For the same mass of substance, gases take up a much bigger space than either a solid or liquid.

3. Volume Shape Compression Flow Solid Definite Incompressible None
Gas Laws
Recall
the kinetic molecular theory states that all matter is composed of particles that are in constant motion
States of Matter
Volume
Shape
Compression
Flow
Solid
Definite
Incompressible
None
Liquid
Indefinite
Yes
Gas
Compressible

4. Common Gases All gaseous elements are non-metals.
There are 3 common classes of gases:
1) Gaseous elements (Ar, He, Kr, etc)
2) Gaseous oxides (CO, CO2, SO2, etc)
3) Gaseous hydrides (H2S, HCl, etc)

5. Kinetic Molecular Theory Cont’d
particles can experience three types of motion
vibrational (back and forth), rotational (spinning) and translational (straight line)
particles in a solid state experience vibrational motion only because the bonds between the molecules are so strong
particles in a liquid state experience all three types of motion (the bonds between particles in a liquid are strong enough to hold it together but not strong enough to create a structure)

6. Kinetic Molecular Theory Cont’d
particles in a gas state experience all three types of motion but experience translational motion to a much greater degree than the particles in the other two states
the result of this increased translational motion is that gases readily diffuse to fill the container they are in
there is no limit to the volume that a gas can occupy, indicating that there are no forces acting between the molecules of a gas

7. Gas Name Chemical Formula Percent Volume Nitrogen N2 78.08% Oxygen O2
Atmospheric Composition
Gas Name
Chemical Formula
Percent Volume
Nitrogen N2
78.08%
Oxygen O2
20.95%
Water
H2O 4%
Argon Ar
0.93%
Carbon Dioxide
CO2
0.0360%
Neon Ne
0.0018%
Helium He
0.0005%
Methane
CH4 %
Hydrogen H2 %
Nitrous Oxide
N2O %
Ozone O3 %

8. Compressed Gases
Liquified gases: these are gases that become liquids when they are under extreme pressure. (hair spray, sodas, etc)
Non-liquified gases: will not liquify under any pressure.
Dissovled gases: the gas is dissolved in a solvent so it will be less dangerous.

9. Gas Pressure Gases exert a pressure, this is called absolute pressure.
Can be measured by a barometer

10. Atmospheric Pressure:
Atmospheric Pressure: the force per unit area exerted by air on all objects within the atmosphere (measured in kPa)
pressure is measured in pascals (Pa)
1 Pa = 1N /m2
the Pascal is a very small unit, so we often work in kilopascals (kPa)
1 kPa = 1000 Pa = 1000 N/m2
at sea level, the atmospheric pressure is kPa
Standard Ambient Temperature and Pressure (SATP) is defined as 25o C and 100 kPa
Standard Temperature and Pressure (STP) is defined as 0oC and kPa

11. Atmospheric Pressure
Pabsolute = Prelative + Patmospheric Atmospheric pressure can be measured by a manometer

12. Units of Pressure
Millimeters of Mercury – mmHg , the early measure of pressure using a barometer.
Torrs – equal to mmHg
Pascals – SI unit! The symbol is Pa, named after Blaise Pascal. This is a very small unit, so kPa are often used.
Bars – one “bar” is equal to 100 kPa
Atmosphere – 1 atm is equal to kPa, this is used when measuring very high pressures.
Pounds per Square Inch – used in some car tire pressure gauges.

13. Measuring Temperature in Kelvin
To measure temperature in chemistry we use the unit of Kelvin rather than degree Celsius.
Kelvin = oC + 273
For example:
0oC = 273 K 25oC = 298 K

14. SATP & STP
From the earliest days of gas measurements, scientists needed some type of standard conditions so that measurements in different units could be compared.
The original values chosen were 0°C (273 K) and 760 mmHg (101.3 kPa). This was called standard temperature and pressure (STP).
In the 1970s this was changed to 25°C and 100 kPa. The name was now changed to standard ambient temperature and pressure (SATP).

15. Gas Laws

16. Boyle’s Law – Pressure and Volume
Boyle’s Law states that the volume and pressure of a gas are inversely proportional, if the temperature and amount of gas remain constant
P1V1 = P2V2
Where: P1 = initial pressure
V1 = initial volume
P2 = final pressure
V2 = final volume 16

17. Ex. 1.2 L of oxygen is placed in a piston in which the initial pressure is kPa. The pressure is increased to kPa. What is the final volume of the gas? 17

18. Charles’ Law – Volume and Temperature
Charles’ Law states that the volume of a gas varies directly with the temperature in Kelvin, if the pressure and amount of gas are constant
V1 / T1 = V2 / T2
Where: T1 = initial temperature (K)
V1 = initial volume
T2 = final temperature (K)
V2 = final volume
NOTE: the temperature for this calculation must be in Kelvin (K) 1 K = 1oC + 273 18

19. Ex. A 100 mL sample of a gas is cooled from. 25oC to 11o C
Ex. A 100 mL sample of a gas is cooled from 25oC to 11o C. What is the final volume? 19

20. Where: T1 = initial temperature (K) P1 = initial pressure
Pressure and Temperature Law – Guy-Lussac’s Law
The Pressure and Temperature Law states that the pressure exerted by a gas varies directly with the absolute temperature, if the volume and amount of gas remain constant
P1 / T1 = P2 / T2
Where: T1 = initial temperature (K)
P1 = initial pressure
T2 = final temperature (K)
P2 = final pressure 20

21. Ex. A tank in a 4º C cooler contains a gas at 875 kPa
Ex. A tank in a 4º C cooler contains a gas at 875 kPa. It is removed from the cooler during the day when the temperature is 29º C. What is the final pressure in the tank? 21

22. Where: P1 = initial pressure V1 = initial volume
Combined Gas Law
The individual gas laws can be combined together to form one law (applies to a constant amount of gas)
(P1V1) / T1 = (P2V2) / T2
Where: P1 = initial pressure
V1 = initial volume
T1 = initial temperature
P2 = final pressure
V2 = final volume
T1 = final temperature 22

23. Practice
Determine the new volume of hydrogen gas if 6.4 L of the gas at kPa and 28oC are moved to a room at SATP.

24. does not condense into a liquid when cooled
Ideal Gas Law
an ideal gas is a hypothetical gas that obeys all gas law perfectly under all conditions
does not condense into a liquid when cooled
graphs of its volume/temperature and pressure/temperature relationships are straight lines
PV = nRT
Where: P = pressure (kPa)
V = volume (L)
n = number of moles (mol)
R = gas constant (8.31 kPaL/molK)
T = temperature (K) 24

25. Ex. What mass of neon gas should be introduced into an evacuated 1
Ex. What mass of neon gas should be introduced into an evacuated 1.0 L tube to produce a pressure of 100 kPa at 30o C? 25