Gas Laws

1
Gas Laws
2
Gas Pressure

• Pressure is defined as force per unit area.
• Gas particles exert pressure when they collide
  with the walls of their container.
• The SI unit of pressure is the pascal (Pa).
• However, there are several units of pressure
• Pascal (Pa)
• Kilopascal (KPa)
• Atmosphere (atm)
• mmHg
• Torr

3
Boyles Law Pressure and Volume

• Boyle was an Irish chemist who studied the
  relationship between volume and pressure
• Boyles law states that the pressure and volume
  of a gas at constant temperature are inversely
  proportional.

4
Boyles Law Pressure and Volume

• At a constant temperature, the pressure exerted
  by a gas depends on the frequency of collisions
  between gas particles and the container.
• If the same number of particles is squeezed into
  a smaller space, the frequency of collisions
  increases, thereby increasing the pressure.

5
Boyles Law Pressure and Volume

• In mathematical terms, this law is expressed as
  follows.
• P1 initial pressure
• V1 initial volume
• P2 final pressure
• V2 final volume
• P1 P2 can be in anything as long as they are
  the same
• V1 V2 can be in anything as long as they are
  the same

6
Example

• A sample of Helium gas is compressed from 4.0 L
  to 2.5 L at a constant temperature. If the
  pressure of the gas in the 4.0 L volume is 210
  KPa, what will the pressure be at 2.5 L?

7
Example

• P1 210 KPa
• P2 ?
• V1 4.0 L
• V2 2.5 L
• P1V1 P2V2
• (210 KPa)(4.0L) (P2)(2.5 L)
• P2 340 KPa

8
Charles Law Volume Temperature

• Charles was a French physicist who looked at the
  relationship between temperature and volume
• He noted that as temperature went up, so did
  volume when pressure was held constant

9
Charles Law Volume Temperature

• This observation is Charless law, which can be
  stated mathematically as follows.

10
Charles Law Volume Temperature

• V1 V2
• T1 T2
• V1 initial volume
• V2 final volume
• T1 initial temperature
• T2 final temperature
• V1 V2 can be in any unit as long as they are
  the same
• T1 T2 MUST be in Kelvin

11
Temperature conversions

• K 273 C
• C 0.56 (F 32)
• F 1.8 C 32

12
Example

• A sample of gas at 40.0 C occupies a volume of
  2.32 L. If the temperature is raised to 75.0 C
  what will the new volume be?

13
Example

• V1 2.32 L
• V2 ?
• T1 40.0 C 313 K
• T2 75.0 C 348 K
• V1 V2
• T1 T2
• 2.32 L V2
• 313K 348 K
• V2 2.58 L

14
Gay Lussacs Law Pressure Temperature

• Gay Lussac studied the relationship between
  pressure and temperature
• He noticed that at a constant volume a direct
  relationship existed between the Kelvin
  temperature and volume
• Giving the equation
• P1 P2
• T1 T2

15
Gay Lussacs Law Pressure Temperature

• P1 P2
• T1 T2
• P1 initial pressure
• P2 final pressure
• T1 initial temperature
• T2 final temperature
• P1 P2 can be in any unit as long as they are
  the same
• T1 T2 MUST be in Kelvin

16
Example

• The pressure of a gas in a tank is 3.20 atm at
  22.0 C. If the temperature rises to 60.0 C,
  what will the new pressure in the tank be?

17
Example

• P1 3.20 atm
• P2 ?
• T1 22.0 C 295 K
• T2 60.0 C 333 K
• P1 P2
• T1 T2
• 3.20 atm P2
• 295K 333K
• P2 3.61 atm

18
Combined Gas Law

• P1V1 P2V2
• T1 T2
• Instead of memorizing all three equations, you
  can simply memorize this one
• Just delete what you don t need

19
Example

• A gas at 110.0 kPa and 30.0C fills a flexible
  container to a volume of 2.00 L. If the
  temperature was raised to 80.0C and the pressure
  was increased to 440.0 kPa, what is the new
  volume?

20
Example

• P1V1 P2V2
• T1 T2
• P1 110.0 kPa
• V1 2.00 L
• T1 30.0 C 303 K
• P2 440.0 kPa
• V2 ?
• T2 80.0 C 353 K

21
Example

• P1V1 P2V2
• T1 T2
• (110.0)(2.00L) (440.0kPa)(V2)
• 303K 353K
• V2 0.583 L