1. UNIT 4: Gases
How can we explain the behavior of gases in terms of pressure?
How can we explain the relationships between P,T, & V? ]

2. Review! Remember gases from the matter unit???
Aim # 1 HOW CAN WE EXPLAIN THE BEHAVIOR OF GASES?
Review! Remember gases from the matter unit???
Gas particles are constantly moving!
They have no Definite Shape or
No Definite Volume

4. Kinetic Molecular Theory
Scientists construct models to explain the behavior of substances
Kinetic Molecular Theory: is a model or theory that is used to explain the behavior of gases

5. KINETIC MOLECULAR THEORY (KMT)
This explains and/or describes the relationships among several variables used to analyze gases
The main variables that we discuss during this topic are pressure (P), volume (V), and temperature (T)

6. There are four major ideas/ assumptions of kmt

7. Kinetic Molecular Theory
Gases contain particles that are in constant, random, straight-line motion.

8. Kinetic molecular theory
2. Gas molecules collide with each other and the walls of their container (exerting pressure). The collisions are considered perfectly elastic ( the particles do not lose energy when they collide)

9. Kinetic Molecular Theory
3. The particles of a gas sample are so small compared to the overall volume the sample occupies. Therefore, the particles’ individual volumes can be ignored (they have negligible volume)

10. KINETIC MOLECULAR THEORY
4. Gas particles do not attract each other at all (do not exhibit intermolecular forces)

11. AIM# 2: HOW CAN WE distinguish between ideal GASES and real gases?
Ideal gas vs. real gas
A gas is said to be “ideal” if it behaves exactly as predicted (kmt)
However, when gases vary from ideal behavior they are called “real gases”

12. Ideal vs. Real Ideal Gases High temperature Low pressure
No attractive forces
No volume
Gases that are smaller and lighter
Ex. H, He
An ideal gas behaves like a real gas if…
Low temp
High pressure
Gases DO have attractive forces
Gases DO have volume
Gases that are bigger and heavier
Ex. Xe

13. PRESSURE LOW IDEAL GAS HIGH TEMPERATURE --- think “IDEAL” vacation
----- Summer – high temperatures, low pressure (no school)

14. AIM # 3: How can we explain the relationships between P,T, & V?
3 WAYS TO MEAUSRE THE BEHAVIOR OF GASES
PRESSURE
TEMPERATURE
VOLUME

15. Pressure
Force per unit area

16. Pressure Units Kilopascal (kPa) Atmosphere (atm)
Millimeters of mercury (mm Hg)
Torr
How to convert between units

17. PRESSURE
Conversion Examples:
2.5 atm to kPa
123.4 kpa to atm

18. STP Standard Temperature and Pressure
Pressure: 1 atm or kPa Temperature: 273 K or 0 °C Table a

19. Aim # 4 how can we explain the relationships between p t and v in terms of gas laws?
The Gas Laws are relationships between temperature, pressure, and volume of a gas. Gas Law equations are used to determine what affect changing one of those variable will have on any of the others.
Gases are unique in that they do not have a definite volume (solids and liquids do!)
That means we change the conditions at which a sample of gas exists (such as pressure around it or the temperature of the gas itself), we can change the volume of the gas sample

20. Gas laws- relationships AMONG VARIABLEs : Pv & t
In order to understand how the variables affect each other we need to keep one of the variables constant
Important assumption  the number of molecules is being kept constant as well (we have a closed container during the experiments)

21. AIM: How can we explain the relationships between P,T, & V?
Charles Law
Boyles Law
Gay – Lussacs Law

22. AIM: How can we explain the relationships between P,T, & V? - PTV trick

23. Boyles LAW - http://www.youtube.com/watch?v=N5xft2fIqQU
As volume decreases, pressure increases (temperature remains constant)

24. Boyle’s Law (P) x (V) ; temperature is constant P1V1=P2V2
Inverse/indirect Relationship

25. Example
A balloon is filled with 25 L of air at 1.0 atm pressure. The pressure is changed to 1.5 atm. What is the new volume?

26. Example
A balloon is filled with 73 L of air at 1.3 atm pressure. What pressure is needed to change to volume to 43 L?

27. Do Now:
There is a government warning on all aerosol cans that states: Do not store at a temperature above 120 F.  Explain why this warning is required in terms of the relationship between temperature and volume.

28. CHARLES LAW - http://www. youtube. com/watch. v=iSK5YlsMv4c http://www
As temperature increases, volume increases and vice versa (pressure remains constant)
Direct relationship

29. Charles’ Law
V1 Pressure is constant T1 V1=V2 T1 T2 **Temperature must be in Kelvin!

30. Example
What volume will 240 mL of a gas occupy if its temperature is raised from 27 °C to 127° C without a change in pressure?

31. Example
At °C a gas has a volume of L. What is the volume of this gas at °C?

32. Gay-Lussac's law https://www. youtube. com/watch. v=kr1V0KtZPGw#t=227
As temperature increases, pressure increases (volume is constant)
Direct relationship

33. Gay-Lussac’s Law P1 Volume is constant T1 P1=P2 T1 T2
**Temperature must be in Kelvin!

34. Example
A cylinder contains a gas which has a pressure of 125kPa at a temperature of 200 K. Find the temperature of the gas when the pressure is 100 kPa.

35. AIM: How can we explain the relationships between P,T, & V
AIM: How can we explain the relationships between P,T, & V? - Combined Gas Law Equation
To solve gas law problems follow the steps:
Make a data table (Temp ALWAYS in Kelvin) P1 P2 V1 V2 T1 T2

36. AIM: How can we explain the relationships between P,T, & V
AIM: How can we explain the relationships between P,T, & V? - Combined Gas Law Equation
Write down the gas law equation
Circle the variable you are trying to solve for, and use basic algebra to rearrange the equation
Eliminate anything that is held constant
Substitute the numbers in the rearranged equation
Round off your answer using sig figs!

37. AIM: How can we explain the relationships between P,T, & V
AIM: How can we explain the relationships between P,T, & V? - Combined Gas Law Equation
1. A 2.00 L sample of gas at STP is heated to 500. K and compress to 200.kPa. What is the new volume of the gas?
2. A 2.00 L sample of gas at 1.00 atm and 300. K is heated to 500. K and compressed to a volume of 1.00 L. What is the new pressure of the gas?

38. AIM: How can we explain the relationships between P,T, & V
AIM: How can we explain the relationships between P,T, & V? - Combined Gas Law Equation
A 2.00 L sample of gas at 300. K and a pressure of kPa is placed into a 1.00 L container at a pressure of 240. kPa. What is the new temperature of the gas?
A sample of gas occupies a volume of 2.00 L at STP. If the pressure is increased to 2.00 atm at constant temperature, what is the new volume of the gas?

39. AIM: How can we explain the relationships between P,T, & V
AIM: How can we explain the relationships between P,T, & V? - Combined Gas Law Equation
A sample of gas occupies a volume of 5.00 L at K. If the temperature is doubled under constant pressure, what will the new volume of the gas be?
A 10.0 L sample of gas in a rigid container at atm and 200. K is heated to 800. K. Assuming that the volume remains constant, what s the new pressure of the gas?

40. GAS BEHAVIOR – Avogadros Hypothesis
Equal volumes of different gases at the same temperature and pressure contain an equal number of molecules/ particles

41. Example
At the same temperature and pressure, which sample contains the same number of moles of particles as 1 liter of O2 (g)?
(1) 1 L Ne(g) (3) 0.5 L SO2 (g)
(2) 2 L N2 (g) (4) 1 L H2O(l)

42. Aim # 5 How can we explain the relationship between vapor pressure and boiling point
VAPOR PRESSURE: the pressure exerted by a liquid’s vapor in a sealed container at a vapor-liquid equilibrium at a given temperature; it is not dependent on the mass or volume of the liquid. The vapor pressure of a liquid can be found on Reference Table H.
The stronger the attractive force between liquid molecules, the lower the vapor pressure is.
Substances with high vapor pressure evaporate quickly, these substances are called volatile

43. Boiling Point
 BOILING POINT: the temperature at which a liquid’s vapor pressure equals the pressure exerted on the liquid by outside forces. Use Reference Table H to determine a liquid’s boiling point. Boiling point increases as exerted pressure is increased.
NORMAL BOILING POINT: the boiling point of a liquid under a pressure of 1.00 atmospheres
** substances with higher boiling points have stronger intermolecular forces, holding the molecules closer together, requiring more energy to overcome the attractive forces **

44. How to Use Table H

45. How to Use Table H

46. AIM: How can we explain the behavior of gases in terms of pressure
AIM: How can we explain the behavior of gases in terms of pressure? – Daltons Law of Partial Pressure
Daltons Law of Partial Pressures: The total pressure exerted by a mixture of gases is equal to the sum of the pressures exerted by each of the gases in the mixture
 PTOTAL = PA + PB + PC + …..

47. AIM# 6: How can we explain the behavior of gases in terms of pressure
AIM# 6: How can we explain the behavior of gases in terms of pressure? – Daltons Law of Partial Pressure
Examples:
What is the total pressure of a mixtures of O2 (g), N2 (g) and NH3 (g) if the pressure of the O2 (g) is 20. kPa, N2 (g) is 60. kPa and the NH3 (g) is 15 kPa?
A mixture of 1 mole of O2 and 2 moles of N2 exerts a pressure of 150 kPa. What is the partial pressure of each gas?