1. Gas Laws

2. Kinetic Theory Particles of matter are ALWAYS in motion.
The volume of individual particles is approximately zero.
Collision of particles with container wall causes pressure.
Particles exert no forces on each other.
The average kinetic energy is approximately equal to the Kelvin temperature of gases.

3. Measuring Pressure
The first device for measuring atmospheric pressure was developed by Evangelista Torricelli during the 17th century
The device was called a “barometer”
baro = weight
meter = measure

4. The Early Barometer
The normal pressure due to the atmosphere at sea level can support a column of mercury that is 760 mm high

5. Modern Day Barometers

6. Pressure Units
Caused by the collisions of molecules colliding with the wall of the container
equal to force/unit area
SI unit = Newton/meter2 = 1 pascal (Pa)
1 standard atmosphere = kPa
1 standard atmosphere = 1 atm = 760 mmHg = 760 torr

7. Definition/Relationship
Pressure Units
Unit
Symbol
Definition/Relationship
Pascal Pa
SI pressure unit
1 Pa = Newton/meter2
Millimeters of mercury
mmHg
Pressure that supports a
1 millimeter column of
mercury in a barometer
Atmosphere
Atm
Average atmospheric
pressure at sea level
and 0° C
Torr
1 torr = 1 mmHg

8. Converting Celsius to Kelvin
For every 1 °C you cool a gas, the volume decreases by 1/273.
–273 °C is absolute zero (0 K) – the coldest temperature possible; all motion ceases.
K = °C
°C = K - 273

9. Standard Temperature and Pressure (STP)
1 atm or 760 mmHg or kPa
Temperature:
0° C or 273 K

10. The Nature of Gases Gases expand to fill their container
Gases are fluid – they flow
Gases have low density
Gases are compressible
Gases effuse and diffuse

11. Boyle’s Law Robert Boyle (1627-1691), Irish chemist
The volume of a given amount of gas held at a constant temperature varies inversely with the pressure. As pressure increases, volume decreases.
P1V1 = P2V2

13. Boyle’s Law Solve the following: 825 Torr = _____ kPa
The volume of oxygen at 120 kPa is 3.20 L.
What is the volume of oxygen at kPa?
101.3 kPa / 760 Torr = x kPa / 825 Torr
kPa = x
P1V1 = P2V2
(120 kPa)(3.20L) = (101.3 kPa)V2
3.79 L = V2

14. Charles’ Law Jacques Charles (1746-1823), French physicist
The volume of a gas varies directly with its absolute temperature. As temperature increases, volume increases.
V1 = V2
T T2

15. Charles’ Law Cont. Solve the following:
The volume of a gas at 40.0 °C is 4.50 L. Find the volume of the gas at 80 °C .
40°C = 313 K °C = 353 K
V1/T1 = V2/T2
4.5L / 313 K = V2 / 353 K
9 L = V2

16. Gay-Lussac’s Law Joseph Gay-Lussac
The pressure of a given mass of gas varies directly with the Kelvin temperature when the volume remains constant.
P1 = P2
T T2
*** Remember – temperature must be in
Kelvin

17. Temp must be in Kelvin, so convert °C to K
Gay-Lussac’s Law
Solve the following:
The pressure of a gas in a tank is 3.20 atm at °C. If the temperature rises to 60.0 °C what will be the gas pressure in the tank?
Temp must be in Kelvin, so convert °C to K
T1 = 22.0 °C = 295K T2 = 60°C = 333K
P1/T1 = P2/T2
3.2 atm / 295K = x atm / 333K
3.61 atm = P2

18. Combined Gas Law
Boyle’s, Charles’s, and Gay Lussac’s laws can be combined into a single law.
The combined gas law states the relationship among pressure, volume, and temperature of a fixed amount of gas.
P1V1 = P2V2
T T2
*** Remember – temperature must be in
Kelvin

19. Convert temp to Kelvin:
Combined Gas Law
Solve the following:
A gas at 110 kPa and 30.0 °C fills a flexible container with an initial volume of 2.00 L. If the temperature is raised to 80.0 °C and the pressure increased to 440 kPa, what is the new volume?
Convert temp to Kelvin:
T1 = 30°C = 303K T2 = 80°C = 353K
P1V1/T1 = P2V2/T2
(110 kPa)(2.00L) / 303K = (440 kPa)V2 / 353K
0.582 L = V2

20. Ideal Gas Law
In all the other gas laws, the relationships hold true for a “fixed mass” or “given amount” of a gas sample.
Because pressure, volume, temperature, and the number of moles present are all interrelated, one equation is used to describe their relationship.
PV = nRT
n = moles
R = ideal gas law constant
V must be in liter
T must be in Kelvin

21. Ideal Gas Law The value of R depends on pressure unit given.
If pressure unit is mm Hg orTorr :
R = L • mm Hg or Torr
mol • K
If pressure is atm:
R = L • atm
If pressure is kPa:
R = L • kPa

22. Ideal Gas Law Solve the following:
44.01 g of CO2 occupies a certain volume at
STP. Find that volume. n = sample mass
molar mass
n = g
g/mol
n = 1 mol
(1atm)(V) = (1mol)(0.0821) (273 K)
V = 22.4 L

23. Ideal Gas Law Solve the following:
Find the molar mass of a gas that weights g and occupies a volume of 250. mL at STP.
(1 atm)(0.250 L) = (n)(0.0821)(273 K)
n = mol
0.011 mol = g X
X = g/mol