1. “The Behavior of Gases”

2. The Properties of Gases

3. Gases can expand to fill its container, unlike solids or liquids
Compressibility
Gases can expand to fill its container, unlike solids or liquids
The reverse is also true:
They are easily compressed, or squeezed into a smaller volume
Compressibility is a measure of how much the volume of matter decreases under pressure

4. Compressibility
This is the idea behind placing “air bags” in automobiles
In an accident, the air compresses more than the steering wheel or dash when you strike it
The impact forces the gas particles closer together, because there is a lot of empty space between them

5. Compressibility
This empty space makes gases good insulators (example: windows, coats)

6. Variables that describe a Gas
The four variables and their common units:
1. pressure (P) in kilopascals
2. volume (V) in Liters
3. temperature (T) in Kelvin
4. amount (n) in moles
The amount of gas, volume, and temperature are factors that affect gas pressure.

7. 1. Amount of Gas
When we inflate a balloon, we are adding gas molecules.
Increasing the number of gas particles increases the number of collisions
thus, the pressure increases
If temperature is constant, then doubling the number of particles doubles the pressure

8. Pressure and the number of molecules are directly related
More molecules means more collisions, and…
Fewer molecules means fewer collisions.
Gases naturally move from areas of high pressure to low pressure, because there is empty space to move into – a spray can is example.

9. 2. Volume of Gas
In a smaller container, the molecules have less room to move.
The particles hit the sides of the container more often.
As volume decreases, pressure increases. (think of a syringe)
Thus, volume and pressure are inversely related to each other

10. 3. Temperature of Gas
Raising the temperature of a gas increases the pressure, if the volume is held constant. (Temp. and Pres. are directly related)
Should you throw an aerosol can into a fire? What could happen?
When should your automobile tire pressure be checked?

11. The Gas Laws

12. The Gas Laws are mathematical
The gas laws will describe HOW gases behave.

13. Robert Boyle ( )

14. #1. Boyle’s Law
Gas pressure is inversely proportional to the volume, when temperature is held constant.
Equation: P1V1 = P2V2 (T = constant) P V

15. Jacques Charles ( )

16. #2. Charles’ Law
The volume of a fixed mass of gas is directly proportional to the Kelvin temperature, when pressure is held constant. V T

17. Converting Celsius to Kelvin
Gas law problems involving temperature will always require that the temperature be in Kelvin. (Remember that no degree sign is shown with the kelvin scale.)
Kelvin = C + 273
°C = Kelvin - 273
and

18. Joseph Louis Gay-Lussac (1778 – 1850)

19. #3. Gay-Lussac’s Law
The pressure and Kelvin temperature of a gas are directly proportional, provided that the volume remains constant. P T

20. #4. The Combined Gas Law
The combined gas law expresses the relationship between pressure, volume and temperature of a fixed amount of gas.

21. The combined gas law contains all the other gas laws!
If the temperature remains constant...

22. Dalton’s Law of Partial Pressures
For a mixture of gases in a container,
PTotal = P1 + P2 + P
P1 represents the “partial pressure”, or the contribution by that gas.

23. Ideal Gases

24. Ideal Gases
A gas with particles that are in constant random motion but have no attraction for each other
Except at very low temp. and very high pressure, most gases behave as ideal gases

25. Avogadro’s Principle
Equal volumes of gases contain equal numbers of moles
at constant temp & pressure
true for any gas
n1/V1 = n2/V2 V n
C. Johannesson

26. Ideal Gas Law Merges the Combined Gas Law with Avogadro’s Principle:
PV=nRT
UNIVERSAL GAS CONSTANT
R= Latm/molK
R=8.315 dm3kPa/molK
You don’t need to memorize these values!

27. Ideal Gas Law Problems P = ? atm n = 0.412 mol T = 16°C = 289 K
Calculate the pressure in atmospheres of mol of He at 16°C & occupying L.
GIVEN:
P = ? atm
n = mol
T = 16°C = 289 K
V = 3.25 L
R = Latm/molK
WORK:
PV = nRT
P(3.25)=(0.412)(0.0821)(289)
L mol Latm/molK K
P = 3.01 atm

28. Practice (on sheet…)
1.00 L of a gas at STP is compressed to 473 mL. What is the new pressure of the gas?
The temperature inside my refrigerator is about 4oC. If I place a balloon in my fridge that initially has a temperature of 22oc and a volume of 0.5 liters, what will be the volume of the balloon when it is fully cooled by my refrigerator?
If I initially have a gas at a pressure of 12 atm, a volume of 23 liters, and a temperature of 200K, and then I raise the pressure to 14 atm and increase the temperature to 300K, what is the new volume of the gas?
If I have 4 moles of a gas at a pressure of 5.6 atm and a volume of 12 liters, what is the temperature?

29. 1. 00 L of a gas at STP is compressed to 473 mL
1.00 L of a gas at STP is compressed to 473 mL. What is the new pressure of the gas?

30. The temperature inside my refrigerator is about 4oC
The temperature inside my refrigerator is about 4oC. If I place a balloon in my fridge that initially has a temperature of 22oc and a volume of 0.5 liters, what will be the volume of the balloon when it is fully cooled by my refrigerator?

31. If I initially have a gas at a pressure of 12 atm, a volume of 23 liters, and a temperature of 200K, and then I raise the pressure to 14 atm and increase the temperature to 300K, what is the new volume of the gas?

32. If I have 4 moles of a gas at a pressure of 5
If I have 4 moles of a gas at a pressure of 5.6 atm and a volume of 12 liters, what is the temperature?