Gas Laws

1
Gas Laws
2
Molecules In The Air

• How do we know there are molecules in the air?
• Has anyone ever had wind burn?
• How about smelled a hamburger when you drove by
  McDonalds?
• These examples demonstrate that air is made up of
  constantly moving molecules.

3
Kinetic Molecular Theory

• Kinetic energy is perfectly maintained in
  elastic molecular collisions.
• Molecules are in constant Motion.
• Vibrational motion.
• Translational motion.
• Tiny particles called molecules make up all
  matter.

4
Kinetic Molecular Theory

• Describes only Ideal Gases
• Ideal gases follow the gas laws in all conditions
  of pressure and temperature.
• Ideal gases assume particles of gas have no
  volume or intermolecular attraction.
• Ideal gases have perfectly elastic molecular
  collisions.

5
In REALITY!

• Real gases have volume.
• Real gases have some intermolecular attraction.
• Real gases can be liquefied and solidified by
  cooling and applying pressure.

• In reality, experimentation shows us that real
  gases do not follow Ideal Behavior

6
Gases Are All Around Us!

• Many gases are invisible, but some we can see.
• Iodine Vapor is Pink.
• Chlorine Gas is Yellow-Green.
• Smoke, clouds, and fog are NOT gases!!

7
Gases Are All Around Us!

• Some gases we can smell.
• Hydrogen Sulfide smells like rotten eggs.
• In natural gas, a smell has been added for our
  protection.
• Other gases we cant smell at all.

8
Gases Are All Around Us!

• Gases have mass.
• Balloons that are filled with air weigh more than
  those that are un-filled.

• When air moves it can do work. For example
  tornadoes or windmills.

9
Gases Are All Around Us!

• Gases occupy space, or have volume.
• Examples
• Inflated Balloon
• Our Lungs
• Scuba Tanks

10
Gas Behaviors

• Compressibility
• The volume of a gas can be decreased by
  increasing the pressure.
• Permeability
• The mixing of molecules in a container.
• Diffusion
• The ability to spread from a high concentration
  to a lower concentration.
• Expansibility
• The ability of a gas to expand and fill a
  container of any size.

11
Under Pressure

• What causes pressure?
• Pressure is caused by the collision of gas
  molecules.
• The molecules can collide with each other or with
  the walls of their container.

12
Atmospheric Pressure

• Air exerts pressure on earth.
• Gravity holds air molecules in the earths
  atmosphere.
• Atmospheric Pressure occurs when those air
  molecules collide with each other or other
  objects.
• Atmospheric pressure decreases as you move to a
  higher elevation.

13
Gas Laws

• There are several different gas law equations.
• Variables
• V
• P
• T
• n
• R
• d
• ?

14
Variables

• V volume in liters.
• T temp in Kelvins.
• P pressure in atm, mmHg, or kPa.
• n number of moles of gas.
• R the universal gas constant.

• d gas density in g/L.
• ? molar mass of a gas in g/mol.

15
Units of Pressure

• Pressure is defined as a force over a specific
  area.
• PF/A
• English system
• lbs/in2 PSI
• Metric system
• N/M2Pascal

16
Boyles Law

• Robert Boyle (1627-1691)
• At a constant temperature, volume and pressure of
  a gas are inversely proportional.

17
Boyles Law

• As pressure increases, volume decreases, and vice
  versa.
• V1P1V2P2
• V œ 1/P
• Remember the volume of a gas can NOT be squeezed
  down to zero!

18
Charless Law

• Jacques Charles (1746-1823)
• At constant pressure, the volume of a gas and
  temperature are directly proportional.

19
Charless Law

• As temperature increases, volume increase, and
  vice versa.
• V1/T1V2/T2
• V œ T
• Gases expand as they get warm , and contract as
  they cool.

20
Gay-Lussacs Law

• Joseph Gay-Lussac (1778-1850)
• At constant volume, gas temperature and pressure
  are directly proportional.

21
Gay-Lussacs Law

• As temperature increases, pressure increases, and
  vice versa.
• P1/T1P2/T2
• T œ P
• This is why aerosol cans say Do not incinerate!

22
Combined Gas

• To simplify life, Boyles Law, Charless Law and
  Gay-Lussacs Law have been put together into one
  mathematical expression.
• Combined Gas Law
• V1P1 V2 P2
• T1 T2