1. Gases
I. Physical Properties

2. A. Properties of Gases Expand to completely fill their container
Take the shape of their container
Low density – mass divided by volume. Take up much more space than their mass.
Much less than solid or liquid state
Compressible
Mixtures of gases are always homogeneous

4. C. Characteristics of Gases
Gases expand to fill any container.
random motion, no attraction
Gases are fluids (like liquids).
except no attraction b/w particles.
Gases have very low densities.
low volume = lots of empty space

5. C. Characteristics of Gases
Gases can be compressed.
low volume = lots of empty space
Gases undergo diffusion & effusion

6. Factors that affect Gases..
Pressure – the force that gas exerts on a given area of a container.
Volume – the space inside a container holding the gas.
Concentrations (Moles) – number of molecules. We convert to mass using molecular weight.
Temperature – the average speed of the gas particles.

7. E. Pressure
Which shoes create the most pressure?

8. Pressure
Pressure of air is measured with a BAROMETER (developed by Torricelli in 1643)
Hg rises in tube until force of Hg (down) balances the force of atmosphere (pushing up).
This is how a straw works. A decrease in pressure inside the straw yields to the atmospheric pressure pushing down and moves the liquid up.

9. Measuring Pressure of a Trapped Gas (cont.)

10. E. Pressure KEY UNITS AT SEA LEVEL 101.325 kPa (kilopascal) 1 atm
760 mm Hg
760 torr
14.7 psi

11. Pressure Conversions A) 2.5 atm = ?kPa B) 200 torr = ? mmHg
C) 30 psi = ?atm
A) 1200 torr = ? atm

12. D. Temperature
Always use absolute temperature (Kelvin) when working with gases. ºF ºC K
-459 32
212
-273
100
273
373
K = ºC + 273

13. Temperature Conversions
A) 10 ºC = ? K
B) 78 ºF = ? ºC
C) 300 K = ? ºC
D) 80 ºF = ? K

14. Standard Temperature & Pressure
F. STP
STP
Standard Temperature & Pressure
273 K
1 atm

15. Boyles’ Law
If the temperature remains constant, the volume and pressure vary inversely
i.e. if P ↑, then V↓; and vice versa
P1 V1 = P2 V2

16. Boyle’s Law (cont.)

17. Boyles’ Law Example
If a gas has a volume of 200ml at 800mmHg pressure, calculate the volume of the same gas at 765mmHg.
P1= 800mmHg
V1= 200ml
P2 =765mmHg
V2=?
Formula P1 V1 = P2 V2

18. Formula P1 V1 = P2 V2
Plug in values
800mmHg x 200ml = 765mmHg x V2
Solve V2= 800mmHg x 200ml
765mmHg
V2 = ml

19. Charles’ Law
If the pressure remains constant, the volume and temperature vary directly
i.e. if T ↑, then V↑; and vice versa
V1 V2
T1 T2 =

20. Charles’ Law (cont.)

21. Charles’ Law Example
The volume of a gas at 20°C is 500ml. Find its volume at standard temperature if the pressure is held constant.
T1= 20°C +273
V1= 500ml
T2 = 0°C +273
V2=?

22. Formula V1 = V2 T1 T2 Plug in values 500ml V2 293K 273K
Solve V2= 273K x 500ml
293K
V2 = ml =

23. Gay Lussac’s Law
If the volume remains constant, the temperature and pressure vary directly
i.e. if P ↑, then T↑; and vice versa
P1 P2
T1 T2 =

24. Pressure and Temperature (cont.)

25. Gay-Lussac’s Example
A steel tank contains a gas at 27°C and a pressure of 12 atm. Determine the gas pressure when the tank is heated to 100°C.
T1= 27°C +273
P1= 12 atm
T2 = 100°C +273
P2=?

26. P1 = P2 T1 T2 Plug in values 12 atm P2 300K 373K
Solve P2= 373K x 12atm
300K
P2 = atm =

27. No, it’s not related to R2D2
Combined Gas Law
The good news is that you don’t have to remember all three gas laws! Since they are all related to each other, we can combine them into a single equation.
P1 V P2 V2 =
T T2
No, it’s not related to R2D2

28. Combined Gas Law
If you should only need one of the other gas laws, you can cover up the item that is constant and you will get that gas law! P1 V1 P2
Boyle’s Law
Charles’ Law
Gay-Lussac’s Law V2 T1 T2

29. Combined Gas Law Problem
A sample of helium gas has a volume of L, a pressure of atm and a temperature of 29°C. What is the new temperature(°C) of the gas at a volume of 90.0 mL and a pressure of 3.20 atm?
Set up Data Table
P1 = atm V1 = .180 L T1 = 302 K
P2 = atm V2= .090 L T2 = ??

30. Calculation
P1 = atm V1 = 180 mL T1 = 302 K
P2 = atm V2= 90 mL T2 = ??
P1 V P2 V2
= P1 V1 T2 = P2 V2 T1
T T2
T2 = P2 V2 T1
P1 V1
T2 = 3.20 atm x mL x 302 K atm x mL
T2 = 604 K = °C
= K

31. Learning Check
A gas has a volume of 675 mL at 35°C and atm pressure. What is the temperature in °C when the gas has a volume of L and a pressure of 802 mm Hg?

32. Ideal Gas Law
By combining the proportionality constants from the gas laws we can write a general equation.
R is called the gas constant.
The value of R depends on the units of P and V.
Generally use R = when Pressure is in atm and Volume is in L
PV = nRT 14

33. T = Temperature (in Kelvin)
Ideal Gas Law PV=nRT
P = Pressure (In atm)
V = Volume (In Liters)
n = Moles (In mol)
R = Gas Constant = 0.082
T = Temperature (in Kelvin)

34. Example 1
A 7.50 liter sealed jar at 18 °C contains moles of oxygen and moles of nitrogen gas. What is the pressure in the container?

35. Example 2
A 4.0 liter container has two gases inside, neon and argon. It is known that at 18 °C, the total pressure of the combined gases is atm. If it is known that there are moles of neon in the container, how many moles of argon are in the container?