1. Essential question: How do chemists describe gases?
Gas Laws
Essential question: How do chemists describe gases?

2. Properties of a Gas Particles in a gas are spread apart
There is no attraction between the gas particles
Gases have no definite volume
Gases fill the container that they are in and take that shape
Contrast this with what you know about solids and liquids

3. Kinetic Theory of Gases Temperature
Temperature is a measure of the average kinetic energy of the particles (KE is the energy of motion)
The hotter a substance becomes the faster the particles move

4. Kinetic Theory of Gases
Gas particles are constantly moving
Particles bounce off each other and the walls of a container
Pressure is related to the amount the particles bounce off the sides of the container

5. There are 3 components of Gases
Pressure
Temperature
Volume

6. Atmospheric Pressure
Atmospheric Pressure: pressure exerted by Earth’s atmosphere; measured by a barometer
Standard atmospheric pressure: column of mercury is 760 mm high at 0oC at sea level 6

7. Pressure Pressure can be measured in Converting
Atmospheres, atm
mm Hg (Torr; another name for mm Hg)
Pascal Pa – kilopascal kPa
Converting
1 atm = 760 mm Hg = kPa
Know how to convert between all three units of pressure

8. Temperature
For gas laws temperature is measured in the Kelvin scale, K
Conversion K = C + 273
Kelvin is an absolute temperature scale
At 0 K there is no movement of particles

9. Standard Pressure and Temperature
Standard pressure and temperature for a gas is 1 atm and 0ºC or 273°K
You will be expected to remember this

10. Volume Volume is measured in liters
Avogadro determined that for any gas at STP will occupy 22.4 liters of space and contain 6.02 x 1023 molecules or atoms

11. Human Gas Particle Activity
You will act as gas particles
You will
Walk in straight lines
When you bump into another “gas particle you will turn and walk in a new direction
You will not
Walk with purpose at another gas particle
Hold on to another gas particle

12. Human Gas Particle Activity
You, as a gas particle, will base you rate of walking based upon temperature
What happens to the rate of movement when temperature changes
I will use a metronome to indicate temperature
Failure to follow the rules will lead to removal from the gas container

13. What happens if we keep T constant
If we lower the pressure volume increases
If we take a balloon up a mountain it will increase because of the lower pressure
If we increase the pressure volume decreases
As we squeeze a balloon it shrinks
This is an inverse relationship

14. Boyle’s Law
When temperature is constant, there is an inverse relationship between pressure and volume
P1V1 = P2V2
Remember, “Boyle at a constant temperature

15. What happens if we keep Pressure constant?
If pressure is constant
If temperature goes up then volume goes up
What happens to a balloon in the sun?
If temperature goes down volume goes down
What happens to a balloon in the winter?
This is a direct relationship

16. Charles Law
Under constant pressure, there is a direct relationship between volume and temperature
V1/T1 = V2/T2
Remember, Charles works under constant pressure

17. What happens we keep Volume constant and change the other two
If we keep volume constant
The pressure will go up if temperature increases
Faster particles will bang against the container more
The pressure will go down if temperature goes down
Slower particles bounce against the container less
This is a direct relationship

18. The Third Law Also named for Gay-Lussac
Under constant volume, there is a direct relationship between temperature and pressure
P1/T1 = P2/T2

19. What happens when more than one variable changes
There are 3 variables to gases
Temperature
Pressure
Volume
If more than one variable changes can you predict the third?
The 3 laws can be combined

20. The Combined Gas Law Boyle’s Charle’s Law The Third Law
P1V1 = P2V2
Charle’s Law
V1/T1 = V2/T2
The Third Law
P1/T1 = P2/T2
Combined they form
P1V1/T1 = P2V2/T2
Can you see all three laws in this one formula?