1. Gas Laws

2. Properties of Gases Gases have no definite shape or volume
They take the shape & volume of whatever container they are in
Balloon, Can, Room, etc.
Gases uniformly fill the container they are in
Gases easily compress or expand

3. Properties of Gases All gases mix completely with any other gas
Example: Air
Nitrogen, Oxygen, Carbon Dioxide, Water Vapor, and others all evenly mixed in our atmosphere

4. Properties of Gases Gases exert pressure on their surroundings
Example: Blowing up a balloon
Air inside pushes against the sides of the balloon and keeps it firm
Example: Puncturing a Pop Can
Carbon Dioxide exerts pressure on the can – puncture allows a place for the gas to escape

5. Pressure Pressure = Force/Area Examples of Pressure:
Carrying something heavy by the handles
A cat walking on you
Tire Pressure

6. Atmospheric pressure
Atmospheric Pressure results from the mass of the air being pulled toward the center of the earth by gravity
Atmospheric Pressure is also known as air pressure
Changes with Altitude– higher pressure at lower altitudes
Changes with weather– temperature & humidity
Cold fronts (high pressure) & Warm fronts (low pressure)
Change in pressure leads to storms

7. Barometer A device that measures atmospheric pressure is a barometer
Atmospheric pressure pushes down on the mercury, pushing it up the tube.
The stronger the atmospheric pressure the higher the mercury gets pushed up the tube

8. Units of pressure There are many units for pressure
1 atm = 760 torr = 760 mm Hg = 101,325 Pascals (Pa) = Kilopascals (kPa) = 14.7 psi
SI unit is atm – make sure all pressure problems and answers have atm as their unit!
Standard atmospheric pressure is 1 atm

9. Cartesian Diver Group activity
What happens when you squeeze the bottle?
Are you increasing or decreasing the pressure in the bottle?
Look closely at the dropper in the bottle, what (other than water) is in the dropper?
When you squeeze the bottle what happens to the volume of the (non-water) contents of the dropper? Is it increasing or decreasing?

10. Boyle’s Law
When the temperature and amount of gas stays the same then the pressure and volume of the gas vary inversely
As pressure increases, volume decreases
As pressure decreases, volume increases
Did this happen with our Cartesian divers?
YES! When we increased the pressure of the container the air bubble got smaller

11. Boyle’s LAW
We should be able to predict what will happen in a problem without even seeing any numbers
Example: If you have a gas and you increase the pressure what happens to the volume?
Example: If you have a gas and you increase the volume what happens to the pressure?

12. Boyle’s Law Equation Boyle’s Law P1V1 = P2V2
P1 = Original Pressure V1 = Original Volume
P2 = New Pressure V2 = New Volume
Pressure is measured in atm
Volume is measured in Liters (L)
If P1V1 = P2V2 then P2 = P1V1 V2 = P1V V2 P2

13. Boyle’s Law Problem #1
Carbon Dioxide is in a pop can and has a pressure of 2 atm and a volume of 0.5L. If you increase the volume to 2L what is the new pressure?
Does this answer make sense?
P1V1 = P2V2 P2= P1V1 V2
P2= (2atm)(0.5L)
2L P2= .5 atm

14. Boyle’s Law problem #2
Freon-12 was once used in refrigerators but has been replaced because it destroys the ozone.
If a 1.5 L sample of freon at a pressure of atm is put under a pressure of 0.2 atm, what would the volume of the gas be?
P1V1 = P2V2
V2= P1V1 P2

15. Boyle’s Law problem #3
A sample of neon has a volume of 2.5 L at a pressure of 0.5 atm, what is the pressure of the neon if it is compressed into a container with a volume of 1 L?
Do you expect pressure to increase or decrease?
Solve the problem

16. Charles’ Law
When the pressure and the amount of gas are kept the same, the volume and temperature of gas are directly proportional
As volume increases, temperature increases
As volume decreases, temperature decreases
Just like Boyle’s Law we can predict what will happen in a problem without even seeing any numbers
If temperature increases what happens to volume?

17. Charles Law Equation Charles Law V1 = V2 T1 T2
V1 = Original Volume T1 = Original Temperature
V2 = New Volume T2 = New Temperature
Volume is measured in Liters (L)
Temperature is measured in Kelvin (K)
If V1 = V2 then V2 = V1T2 and T2 = V2T1
T1 T T V1

18. Charles’ Law and Absolute Zero
Charles did an experiment to cool several different gases. Obviously there was a problem since at some temperature the gases would liquefy.
However, when he extrapolated the data, all lines converged on a certain temperature (right around -273°C)
Kelvin took up on this idea and decided to make a new temperature scale and start absolute zero at zero.

19. Absolute Zero All gas law problems must be in Kelvin!!!!
Kelvin = oC + 273
Example What is the Kelvin temperature of
-30oC?
K= = 243
Temperature = 243 K

20. Charles’ Law #1
A sample of gas at 288K has a volume of 2 L. The temperature is raised to 300K. What is the new volume?
Does this make sense?
V1 = V2 V2 = V1T2
T1 T T1
V2= (2L)(300K) V2= 2.08L
288K

21. Charles’ Law #2
A sample of gas at 300K has a volume of 1.5L and the temperature is lowered to 250K What is the new volume?
V1 = V2
T1 T2
V2 = V1T2 T1

22. Charles’ Law Problem #3
A 2.0 Liter sample of air is collected at 298K and then cooled to 278 K.
Do you expect the volume increase or decrease?
What is the new volume?

23. Combined Gas Law
Combining Boyle’s and Charles’ Laws (but keeping the amount of gas constant) you get:
P1V1 = P2V2
T T2
Use this Law when Pressure, Volume, and temperature are all changing

24. Combined Gas Law
P1V1 = P2V2 can be rearranged to solve for… T1 T2 P2 = P1V1T2 Pressure is in atm T1V2 V2 = P1V1T2 Volume is in Liters (L) T1P2 T2 = P2V2T1 Temperature is in Kelvin (K) P1V1

25. Combined Gas Law Problem #1
If a 5.0 L sample of gas at 295K and 3.0 atm pressure is cooled to 275K and the pressure is decreased to 2.0 atm, what is the new volume of the gas?
V1= 5 P1= 3 T1= 295 P2= 2 T2=275
V2 = P1V1T2 V2 = (3)(5)(275) V=6.99L
T1P2 (295)(2)

26. Combined Gas Law Problem #2
If a 2 L sample of gas at 300K and 5.0 atm pressure is cooled to 250K and the volume is decreased to 1 L, what is the new pressure of the gas?
V1= P1= T1= V2= T2=
P2 = P1V1T2
T1V2

27. Combined Gas Law Problem #3
A 8 L sample of gas at 295K and 3.0 atm gets its volume decreased to 3 L and the pressure increased to 5 atm, what is the new temperature?

28. PV = nRT Ideal Gas Law P = Pressure in atm V = Volume in Liters (L)
T = Temperature in Kelvin (K)
n = the number of moles of gas
R = Universal Gas Constant = L·atm mol·K
Notice the units for R, all Ideal Gas Law problems must be in these units!!!

29. Ideal Gas Law
PV = nRT
P = nRT V = nRT
V P
n = RT T = PV
PV nR

30. Ideal Gas Law Problem #1
A sample of Hydrogen gas has a volume of 8.5 L at a temperature of 275K and a pressure of 1.5 atm. How many moles of gas are present? R= T=275 P=1.5 V=8.5 n = RT n = (0.0821)(275) 1.77 moles PV (1.5)(8.5)

31. Ideal Gas Law Problem #2
2.5 moles of Carbon Dioxide has a volume of 3L and a temperature of 300K. What is the pressure of the gas? R= n= T= V= P = nRT V

32. Ideal Gas Law Problem #3
What volume is occupied by 10 moles of Carbon Monoxide at 295K and 0.5 atm? R= n= T= P=

33. Ideal Gas Law Problem #4
What temperature is 5 moles of Oxygen that has a volume of 6 L and a pressure of 0.2 atm?

34. STP Sometimes there’s a shortcut!
STP stands for “Standard Temperature and Pressure”
STP is 1 atm and 273K
At STP, 1 mole of any gas has a volume of 22.4L

35. Ideal Gas Law Problem #5
How many moles of Nitrogen are present in 1.0L of gas at STP?

36. Dalton’s Law of Partial Pressure
Remember that gases mix evenly
The pressure of the mixture is equal to the pressure of each individual gas added up
Pressure (total) = Pgas Pgas Pgas3 +…

37. Dalton’s Law Problem #1
Mixtures of Helium and Oxygen are used in the “air” tanks of underwater divers. If 12L of O2 and 46L of Helium are in a 5.0L tank at 295K and 1.0atm, what is the partial pressure of each gas? P = nRT P0xygen = ( V

38. Dalton’s Law Problem #2
A 2.0 L flask contains a mixture of 0.05 moles nitrogen and moles of oxygen gas at 295K. The total pressure in the container is 0.91 atm. What is the partial pressure of each gas in the container?

39. Dalton’s Law Problem #3
A 3L container with 1 mole of Helium and 0.20 moles of Fluorine gas at 300K. What is the partial pressure of each gas is in the container?