1. Characteristic of Gases

2. The Nature of Gases Gases expand to fill their containers
Gases are fluid – they flow
Gases have low density
1/1000 the density of the equivalent liquid or solid
Gases are compressible
Gases effuse and diffuse

3. Gases Are Fluids Gases are considered fluids.
The word fluid means “any substance that can flow.”
Gas particles can flow because they are relatively far apart and therefore are able to move past each other easily.

4. Gases Have Low Density
Gases have much lower densities than liquids and solids do - WHY?
Because of the relatively large distances between gas particles, most of the volume occupied by a gas is empty space.
The low density of gases also means that gas particles travel relatively long distances before colliding with each other.

5. Gases are Highly Compressible
Suppose you completely fill a syringe with liquid and try to push the plunger in when the opening is plugged.
You cannot make the space the liquid takes up become smaller.
The space occupied by the gas particles is very small compared with the total volume of the gas.
Applying a small pressure will move the gas particles closer together and will decrease the volume.

6. Gases Completely Fill a Container
A solid has a certain shape and volume.
A liquid has a certain volume but takes the shape of the lower part of its container.
In contrast, a gas completely fills its container.
Gas particles are constantly moving at high speeds and are far apart enough that they do not attract each other as much as particles of solids and liquids do.
Therefore, a gas expands to fill the entire volume available.

7. Gas Pressure

8. Gas Pressure
Earth’s atmosphere, commonly known as air, is a mixture of gases: mainly nitrogen and oxygen.
As gas molecules are pulled toward the surface of Earth, they collide with each other and with the surface of Earth more often. Collisions of gas molecules are what cause air pressure.

9. Standard Temperature Pressure (STP)
Measuring Pressure
Force
Newton (N)
Pressure =
Area
m2, cm2
Units of Pressure
1 atm = 760 torr = kPa = 760 mmHg
Standard Temperature Pressure (STP)
1 atm, 0°C , 22.4 L , 1 mole

10. 1. Covert 1.00 atm to mmHg
1.00 atm
760 mmHg
= 7.60 x 10^2 mmHg
1 atm
2. Covert 3.00 atm to kPa.
3.00atm
101.3 kPa
= 304 kPa
1 atm
3. What is KPa in atm?
1 atm
100.0 kPa
= atm
101.3 kPa

11. Measuring Pressure Using Barometer
Measures atmospheric pressure
The atmosphere exerts pressure on the surface of mercury in the dish.
This pressure goes through the fluid and up the column of mercury.
The mercury settles at a point where the pressure exerted downward by its weight equals the pressure exerted by the atmosphere.

12. Gas Theory

13. Kinetic Molecular Theory
Particles of matter are ALWAYS in motion
Volume of individual particles is  zero.
Collisions of particles with container walls cause pressure exerted by gas.
Particles exert no forces on each other.
Average kinetic energy is proportional to Kelvin, temperature of a gas.
Ideal gas- imaginary perfect
gas fitting the theory

14. Checking for understanding
List 5 characteristics of gases: 1. 2. 3. 4. 5.
List 5 characteristics of gases according to the KMT:

15. Gas Laws

16. Gases are described by their measurable properties.
Measurable Properties of Gases
Gases are described by their measurable properties.
P = pressure exerted by the gas
V = total volume occupied by the gas
T = temperature of the gas
n = number of moles of the gas
Units
atm L K
mol

17. **Gas Laws – ABCGG LAWS**
n is proportional to constant T
vogadro’s A B C G
oyles’s
P is inversely proportional to constant T
V is proportional to constant P
harles’s
ay- Lussac’s
P is proportional to constant V
Rate of effusion is inversely proportional to square root of gas’s molar mass
raham’s

18. Pressure-Volume Relationship : Boyle’s Law
Pressure and Volume are inversely proportional at constant temperature
 Pressure =  Volume
 Volume =  Pressure
PV = k
P1V 1= P2V2

19. For ALL calculations!!!
Circle the numbers, underline what you are looking for.
Make a list of number you circled using variables.
Write down the formula
Derive the formula to isolate the variable you are looking for.
Plug in the numbers
Answer according to significant figures

20. Boyle’s Law Calculation
A given sample of gas occupies 523mL at 1.00 atm. The pressure is increased to 1.97 atm while the temperature stays the same. What is the new volume of the gas?
P1= 1.00 atm
P2= 1.97 atm
V1= 523 mL
V2= ? mL
P1V 1= P2V2
P1V1
(1.00 atm) (523 mL)
V2= = P2
(1.97 atm) =
265 mL

21. 1. A sample of oxygen gas has a volume of 150. 0mL at a pressure of 0
1. A sample of oxygen gas has a volume of 150.0mL at a pressure of atm. What will the volume of the gas be at a pressure of 1.00 atm if the temperature remains constant?
P1= atm
P2= 1.00 atm
V1= mL
V2= ? mL
P1V 1= P2V2
P1V1
(0.947atm) (150.0 mL)
V2= = P2
(1.00atm) =
142mL

22. 2. If 2. 5 L of a gas at 110. 0 kPa is expanded to 4
2. If 2.5 L of a gas at kPa is expanded to 4.0 L at constant temperature, what will be the new value of pressure?
P1=110.0 kPa
P2= ? kPa
V1= 2.5 L
V2= 4.0 L
P1V 1= P2V2
P1V1
(110.0 kPa) ( 2.5 L)
P2= = V2
(4.0 L) =
69 kPa

23. Temeperature-Volume Relationship: Charle’s Law
Volume and temperature are proportional at constant pressure
 volume =  temperature (K)
 Volume =  temperature (K)
 KE of the gases,   temperature V
= k T V1 T1 = V2 T2

24. Charles's Law Calculation
A balloon is inflated to 665 mL volume at 27°C. It is immersed in a dry-ice bath at −78.5°C. What is its volume, assuming the pressure remains constant?
V1= 665 mL
V2= ? mL
T1= 27°C K
= 300 K
T2= -78.5°C K
= K V1 V2 = T1 T2 V1 T2
(665 mL)( K) V2 = = T1
(300 K)
4.3 x 10^2 mL =

25. 1. Helium gas in a balloon occupies 2. 5 L at 300. 0K
1. Helium gas in a balloon occupies 2.5 L at 300.0K. The balloon is dipped into liquid nitrogen that is at a temperature of 80.0K. What will be volume of the helium in the balloon at the lower temperature be?
V1= 2.5 L
V2= ? mL
T1= 300 K
T2= 80.0 K V1 V2 = T1 T2 V1 T2
(2.5 L)( 80.0 K) V2 = = T1
(300 K) =
0.67 L

26. 2. A helium filled balloon has a volume of 2. 75 L at 20. 0 °C
2. A helium filled balloon has a volume of 2.75 L at 20.0 °C . The volume of the balloon changes to 2.46 L when placed outside on a cold day. What is the temperature outside in °C ?
V1= 2.75 L
V2= 2.46 L
T1= 20 °C K = 293 K
T2= ? °C V1 V2 = T1 T2 V2 T1
(2.46 L)( 293 K ) T2 = = V1
(2.75 L) =
K = °C = °C

27. Temperature-Pressure Relationships: Gay-Lussac’s Law
Pressure and temperature are proportional at constant volume
 pressure =  temperature (K)
 pressure =  temperature (K) P
= k T P1 T1 = P2 T2

28. Gay-Lussac’s Law Calculation
1. An aerosol can containing gas at 101 kPa and 22°C is heated to 55°C. Calculate the pressure in the heated can.
P1= 101 kPa
P2= ? kPa
T1= 22 °C K = 295 K
T2= 55 °C + 273K = 328 K P1 P2 = T1 T2 P1 T2
(101 kPa)( 328 K ) P2 = = T1
(295 K) =
1.1 x 10^2 kPa

29. 2. A sample of helium gas is at 122 kPa and 22°C
2. A sample of helium gas is at 122 kPa and 22°C. Assuming constant volume. What will the temperature be when the pressure is 203 kPa?
P1= 122 kPa
P2= 203 kPa
T1= 22 °C K = 295 K
T2= ? K P1 P2 = T1 T2 P2 T1
(203 kPa)(295K) T2 = = P1
(122 kPa) =
4.9 x 10^2 K or 2.2 x10^2 °C

30. Volume-Molar Relationships: Avogadro’s Law
Volume and number of moles (n) are proportional at constant temperature and pressure
 volume =  number of moles
 volume =  number of moles
22.4 L for 1 mole of a STP V1 n1 = V2 n2 V
= k n

31. Avogadro’s Law
What volume of CO2 contains the same number of molecules as 20.0mL of O2 at the same conditions?
20 mL

32. Gas Laws
Combined Gas Law

33. Checking for understanding
State the law
Explain the law in your own words
Write the formula(s)
Boyle’s Law
Charle’s Law
Gay-Lussac’s Law
Avogadro’s Law

34. Gas Behavior – Diffusion/Effusion
Diffusion is the movement of particles from regions of higher density to regions of lower density.
The passage of gas particles through a small opening is called effusion.

35. Effusion

36. Graham’s Law
The molecular speeds, vA and vB, of gases A and B can be compared according to Graham’s law of diffusion shown below.
Graham’s law of diffusion states that the rate of diffusion of a gas is inversely proportional to the square root of the gas’s molar mass.
Particles of low molar mass travel faster than heavier particles.

37. Graham’s Law Calculation
At the same temperature, which molecule travels faster O2 or H2?
= 3.98
Hydrogen travels 3.98 times faster than oxygen.

38. Graham’s Law Calculation
Oxygen molecules have a rate of about 480 m/s at room temperature. At the same temperature, what is the rate of molecules of sulfur hexafluoride, SF6?
rO2 = 480 m/s
MO2 = 32g
rSF6= ? m/s
MSF6= 146g
= 220 m/s

39. Dalton’s Law Ptotal = PA + PB + PC
The pressure of each gas in a mixture is called the partial pressure.
The total pressure of a mixture of gases is the sum of the partial pressures of the gases. This principle is known as Dalton’s law of partial pressure.
Ptotal = PA + PB + PC

40. Dalton’s Law Calculation
What is the total pressure in a balloon filled with air (O2 & N2) if the pressure of the oxygen is 170 mm Hg and the pressure of nitrogen is 620 mm Hg?
Ptotal = PA + PB + PC…..
Ptotal = POxygen + Pnitrogen
= 170 mmHg mmHg
= 790 mmHg

41. Checking for understanding
State the law
Explain the law in your own words
Write the formula(s)
Graham’s Law
Dalton’s Law

42. Ideal Gas

43. Molecular Composition of Gases
No gas perfectly obeys all four of these laws under all conditions.
These assumptions work well for most gases and most conditions.
One way to model a gas’s behavior is to assume that the gas is an ideal gas that perfectly follows these laws.
An ideal gas, unlike a real gas,
does not condense to a liquid at low temperatures,
does not have forces of attraction or repulsion between the particles, and is
composed of particles that have no volume.

44. Ideal Gas Law
The combined gas law expresses the relationship between pressure, volume and temperature of a fixed amount of gas.
PV = nRT
P = pressure in atm
V = volume in liters
n = moles
R = proportionality constant
= L atm/ mol·K
T = temperature in Kelvins

45. Ideal Gas Law Calculation
How many moles of gas are contained in 22.4 L liter at 100. atm and 283K?
PV = nRT
P = 100 atm
V = 22.4 L
n = ? Moles
R = L·atm/mol· K
T = 283 K PV
n = RT
(100 atm)(22.4L) =
( L·atm/mol· K) ( 283 K)
=96.4 moles

46. Calculate the pressure exerted by 43 mol of nitrogen in a 65L of cylinder at 5.0°C.
P = ? atm V = 65 L
n = 43 mol R = L·atm/mol· K
T = 5°C + 273K = 278 K
PV = nRT
nRT
P = V
(43 mol)( L·atm/mol· K) ( 278 K) =
(65 L)
=15 atm

47. What will be the volume of 111 mol of nitrogen where the temperature is -57°C and pressure is 250 atm?
P = 250 atm V = ? L
n = 111 mol R = L·atm/mol· K
T = -57°C + 273K = 216 K
PV = nRT
nRT
V = P
(111 mol)( L·atm/mol· K) ( 216 K) =
(250 atm)
=7.9 L

48. Checking for understanding
Explain how is ideal gas different from a normal gas.
2. Write the formula for ideal gas
3. What variables can be determined by using the formula?