1. Gas Laws

2. Gas Laws General Info
Gas laws tell us what the relationships are between pressure, volume, and temperature
Units , Units, Units
There are several different gas laws, you do not need to memorize the names
STP
Kelvin – YOU MUST USE THE KELVIN TEMPERATURE SCALE FOR ALL GAS LAW PROBLEMS
Kelvin is an absolute temperature scale

3. k represents a constant
PV = nRT
PV = k if ……
P/T = k if …….
V/T = k if …….

4. A balloon that occupies 0
A balloon that occupies 0.54L at 27C is put in the freezer at 0C, what is the new volume?
As a hot air balloon is heated the atmospheric pressure remains unchanged. What will happen to the volume of the balloon?

5. A gas bottle at room temperature is used to fill helium balloons
A gas bottle at room temperature is used to fill helium balloons. When the gas is let out of the bottle the pressure on the gas decreases, what will happen to the volume of the gas?
Gas in a piston has a pressure of 1.2 atm and a volume of 0.032L. What will the volume be after the piston moves and changes the pressure to 2.7 atm?

6. A gas in a sealed, rigid container is heated
A gas in a sealed, rigid container is heated. How will the pressure change?
A gas in sealed, rigid container is heated from 23C to 35C. If the original pressure was 1.4 atm, what is the new pressure in mmhg?

7. Dalton’s Law of partial pressures
A mixture of Helium, Argon, and Oxygen has a total pressure of 5.6atm. There are 3.1atm of oxygen and 0.3atm of argon. What is the pressure of the helium?

8. Ideal gas law
PV = nRT
This is a way to relate P V T to moles. This assumes all gases act the same under the same conditions (mostly true).
Look at the unit of pressure to choose the correct value for R
Write all units

9. Pressure Pressure is a force over an area What causes pressure?
Gas molecules colliding with the inside of a container
What are some changes you could make to system to decrease pressure?
PHET Simulation – you will be using this tomorrow

10. Kinetic Molecular theory (for gases)
Gas molecules are in constant random motion
Gas molecules move in straight lines until they hit something
Gas molecules have perfectly elastic collisions
Which molecules in the simulation have more energy, the large molecules or the small ones?

11. Gas stoichiometry
At STP we can convert directly from moles to L by using 22.4L = 1 mol
You have 4 moles of helium gas at STP, what is the volume of the gas?
You have an unknown amount of HCl gas at STP, if the gas occupies 4.5L how many grams do you have.

12. Partial Pressure
Pressure can be used as a representation of concentration for gases because the more gas you have the higher the pressure goes. The pressure of one gas in a mixture is called the partial pressure of that gas.
The partial pressures in a gas mixture are: hydrogen (0.54atm), oxygen (0.86atm), and helium (0.23atm). If the temperature is 25C and the volume of the container is 2.3L how many moles of hydrogen are present?
How many grams of hydrogen are present?

13. Gas stoichiometry
You are given the equation for the combustion of methane. If 22.6L of methane reacts with excess oxygen how many liters of carbon dioxide will be produced?
Under the same conditions, all gases act the same. This is not true for liquids or solids. The molecules of a gas are very far apart relative to their sizes so all gases are mostly empty space. The size of the gas molecule does not matter.
Use the sample problem above and sample problem H on p 370 to work practice problems 1-3 on page 370
Next work p373 practice #1,2,
Finally p373 formative assessment #2,4,6

14. The constant random motion of gas particles cause the molecules to spread out.
Diffusion – the process by which gas particles disperse
Effusion – the process by which gas particles in a container randomly pass through a tiny opening in a container.
How will the size of the molecule affect the rate of effusion and diffusion?