1. Gas Laws
Lesson 1: Da Procida

2. Pressure = Force Area We control pressure of a gas with a piston.
If we increase or decrease pressure of a gas, we see different behaviors.
Measured in atmospheres (atm) or Pascales (Pa)

3. Volume The amount of space a gas occupies.
Generally measured in liters (L) or meters- cubed. (m^3)

4. Temperature
How hot or cold a gas is.
Often measured in Kelvins.

5. Concept Question
In a given gas, how do you think pressure and volume relate? (Pretend temperature is constant)
♣ P ~ V
♣ P ~ 1/V
♣ P ~ kV (for some constant k)
♣ I don’t know.

6. Concept Question Next, let’s look at volume and temperature.
(constant P)
♣ V ~ T
♣ V ~ 1/T
♣ V ~ T^2
♣ I don’t know.

7. Concept Question For constant V, how do P and V relate? ♣ P ~ V
♣ No relation
♣ I don’t know.

8. Ideal Gas Law
PV = nRT
• An ideal gas means that this is an approximation – it will not work perfectly particularly at high pressure and temperature.
• R = Avogadro’s constant = 8.31J/molK or .082atmL/molK
• n = the number of moles of a gas.
A mole has exactly 6.02x23 molecules.
A mole of carbon is a different weight than a mole of hydrogen.
On the periodic table of elements, we have the molecular weight, which tells us how much one mole of that element weighs.

9. Practice Problems
1) If 25.5 mol of helium gas is at 10C and a pressure of 136kPa, what is the volume of the gas under these conditions?
What is the temperature if the gas is compressed to precisely half the volume at a gauge pressure of 101 kPa?

10. Practice Problems
2) A storage tank contains 21.6kg of nitrogen (N2) at an absolute pressure of 3.65 atm. What will the pressure be if the nitrogen is replaced by an equal mass of CO2?
Molecular mass of Nitrogen = .014 kg/mole
Molecular mass of Carbon: .012 kg/mole
Molecular mass of Oxygen: .016 kg/mole
R = 8.31 atm-L / mol-K

11. Practice Problems
3) An air bubble at the bottom of a lake 43.5m deep has a volume of 1cm^3.
If the temperature at the bottom of the lake is 5.5C and the temperature at the top is 21C, what is the volume of the bubble just before it reaches the surface?
Degrees Kelvins = Degrees C
1 atm = 101kPa = 101,000 Pa
1cm^3 = 1 x 10^-6 m^3