Gases

1
Gases

• Chapter 11

2
Kinetic Theory and Gas Properties

• The kinetic theory assumes that
• Volume of gas particles is insignificant
• There is space between gas particles
• Gas particles do not attract or repel each other
• Gas particles move rapidly and in constant random
  motion

3
Variables that Describe a Gas

• Pressure (atm, mmHg, kPa)
• Volume (L)
• Temperature (C or K)
• Number of moles (mol)

4
What happens if you

• decrease the volume of the container?
• Pressure may increase
• Temperature may increase
• increase the temperature?
• Pressure may increase
• Volume may increase
• Increase the pressure?
• Temperature may increase
• Volume may decrease

5
Gas Laws

• Boyles
• P1 x V1 P2 x V2
• Charles
• V1 V2
• T1 T2
• Gay-Lussac
• P1 P2
• T1 T2

6
How do we tie it all together?

• P1V1 P2V2
• T1 T2
• AKA
• The Combined Gas Law
• Allows you to predict what will happen to a gas
  if some of the conditions change!

7
Lets Practice!

• A gas with a volume of 4.0L at 90.0kPa expands
  until the pressure drops to 20.0kPa. What is the
  new volume if the temperature remains constant?
• Identify what you know
• V14.0L
• P190.0kPa
• P220.0kPa
• T1T2
• Solve for what you dont know
• V2 P1V1 x T2
• T1 P2
• V2 18L

8
Now you try!

• A gas with a volume of 3.00x102mL at 150.0C is
  heated until its volume is 6.00x102mL.What is the
  new temperature of the gas if the pressure
  remains constant at 1.0 atm during the heating.
• T2 T1 x P2V2
• P1V1
• T2 300C

9
Ideal Gases vs. Real Gases

• Particles have no volume
• Particles are not attracted or repelled to each
  other
• Ideal gases can never be liquefied or solidified

• Particles have volume
• Particles experience intermolecular forces
• Real gases can be liquefied and solidified

10
Real Gases Act Like Ideal Gases

• When temperatures are very high and pressures are
  very low
• Can you explain why?
• High Temperatures means lots of kinetic energy so
  particles are moving rapidly and randomly
• Low Pressures means particles do not hit the
  container (and each other) often, so they cannot
  feel attraction and repulsion

11
The Ideal Gas Law

• Allows us to solve for a property of an ideal gas
  when properties are constant!
• PVnRT
• Ppressure Vvolume Ttemperature
• nnumber of moles
• R 8.31 L x kPa or 0.08206 L x atm
• K x mol K x mol

12
Lets Practice

• Determine the volume occupied by 0.582 mol of a
  gas at 15C if the pressure is 81.1 kPa.
• Identify what you know
• n0.582 mol
• T15C 273 288 K
• P81.1 kPa.
• R 8.31 L x kPa / K x mol
• V17 L

13
When to use the equations

• If the conditions of the gas change
• Then use the combined gas law
• If the conditions of the gas are fixed
• Then use the ideal gas law