1. Gases, Liquids, and Solids
Chapter Seven
Gases, Liquids,
and Solids

2. Kinetic Molecular Theory.
Theory developed to explain physical behavior of the ______ states of matter (solid, liquid, and gas)
Theory of _________ molecules.

3. Assumptions of KMT
Matter is composed of _____ particles (atoms, molecules or ions) that have definite and characteristic sizes that do not change.
The particles are in constant, random _________ and therefore possess kinetic energy (energy of _______).
The particles interact with one another through attractions and repulsions and therefore possess _____________ energy.
The _______ of the particles (and their kinetic energy) increases as the _____________ is increased.
The particles in a system ___________ energy to each other through elastic collisions.

4. Gases, Liquids, and Solids cont’d
Figure (a) In a solid, the particles (atoms, molecules, or ions) are close together and vibrate about fixed sites. (b) The particles in a liquid, though still close together, freely slide over one another. (c) In a gas, the particles are in constant random motion, each particle being independent of the others present.

5. Solid State
Characterized by a dominance of __________ energy over ____________ energy
There are strong forces that hold individual molecules together
Low kinetic energy = little motion of molecules
Particles in a solid are tightly packed together in a definite arrangement
Consequences:
___________ volume and ______________ shape
High density
Small compressibility

6. Liquid State
Characterized by __________ energy and _________ energy that are approximately __________ in magnitude
Particles in a liquid are randomly packed, touching each other, and have enough kinetic energy that they constantly slide over each other.
Consequences:
___________ volume and ____________ shape
High density
Small compressibility
Small thermal expansion

7. Gaseous State
Characterized by dominance of ________ energy over ______________ energy
Gas particles have enough kinetic energy to move far apart from each other (moving in straight lines)
There is very little attraction between particles
Consequences:
___________ volume and _____________ shape
Low density
Large compressibility
Moderate Thermal Expansion

8. Gases move in straight lines
Atoms or molecules bounce off each other and the sides or walls of container.

9. Gases, Liquids, and Solids cont’d

10. Gases, Liquids, and Solids cont’d
Fig. 7.5
When a gas is compressed, the amount of empty space in the container is decreased.

11. Four Important Gas Variables
1. n = number of moles
n = mass/MM
2. T = temperature; must be in Kelvin!
K = oC
3. V = Volume, usually measured in Liters
1000 mL = 1 L
4. P = Pressure = force/area
1 atm = 760 mm Hg = 760 torr = lb/in2 = Pa
Pressure of a gas results from the number of collisions per unit time on the walls of container.

12. Two Important Relationships
Directly proportional: if the value of one variable increases, the value of the other variable also increases
Inversely proportional: if the value of one variable increases, the value of the other variable decreases

13. Relationship Between Pressure and Volume (Boyle’s Law)
When the pressure is increased on a gas, its volume goes down – inversely proportional!

14. Gases, Liquids, and Solids cont’d
Fig When the volume of a gas at constant temperature decreases by half, the average number of times a molecule hits the container walls is doubled.

15. Volume/Pressure Calculation
A balloon is inflated to a volume of 12.6L on a day when the atmospheric pressure is 675 mm Hg. The next day, a storm drops the pressure to 651 mm Hg. Assuming constant temperature, what is the new volume of the balloon?

16. Relationship Between Temperature and Volume (Charles’ Law)
When the temperature is increased on a gas, its volume goes up – directly proportional!
KELVIN !!!

17. Volume/Temperature Calculation
The volume of a sample of air at 30. oC is 3.50 L. Assume that the pressure is held constant. What would be the volume of air at 300. oC?

18. Combined Gas Laws
Relates the changes in pressure, volume and temperature of a gas

19. Combined Gas Law Practice
A fixed quantity of nitrogen gas in a 275 mL container at a pressure of 625 mm Hg is transferred to a container with a volume of 750. mL. What is the new pressure if the temperature changes from 25 oC to 17 oC?

20. The Ideal Gas Law
Describes the relationships among the four variables for gaseous substances: P, T, V, n
PV = nRT
R is called the ideal gas constant
L·atm/mol·K
Always make sure you have all your units correct!

21. Ideal Gas Law Calculations
Methane, CH4, can be used as fuel for an automobile; however, it is a gas at normal temperatures and pressures, which causes some problems with storage. One gallon of gasoline could be replaced by 655 g of CH4. What is the volume of this much methane at 25 oC and 745 mm Hg.

22. Ideal Gas Law Calculations, II
What is the temperature (in oC) of a sample of 3.00 moles of He at 27.5 atm of pressure and in a 6.00 L container?

23. Dalton’s Law of Partial Pressures
Since gas molecules are so far apart, we can assume they behave independently.
Dalton’s Law: in a gas mixture the total pressure is given by the sum of partial pressures of each component:
Partial Pressure
The pressure that a gas in a mixture of gases would exert if it were present alone under the same conditions

24. Figure A set of four containers can be used to illustrate Dalton's law of partial pressures. The pressure in the fourth container (the mixture of gases) is equal to the sum of the pressures in the first three containers (the individual gases).

25. Dalton’s Law Calculation
A mixture of H2, N2 and Ar gases is present in a steel cylinder. The total pressure within the cylinder is 675 mm Hg and the partial pressures of N2 and Ar are, respectively, 354 mm Hg and 235 mm Hg. If CO2 gas is added to the mixture, at constant temperature, until the total pressure reaches 842 mm Hg, what is the partial pressure, in mm Hg, of the following?
A) CO2 B) N2 C) Ar D) H2

27. Gas Laws Some common examples illustrating applications of gas laws.
Filling a syringe
Popping corn
Use of dynamite

28. Gases, Liquids, and Solids cont’d
Fig. 7.10
Filling a syringe with a liquid is an application of Boyle’s law.

29. Gases, Liquids, and Solids cont’d
CC 7.1
Phil Degginger/Color-Pic

30. Rapid Expansion of Gases
4 C3H5O3(NO2)3(s) →
12 CO2(g) + 10 H2O(g) + 6 N2(g) + O2(g)
_________________ reaction takes place in a small confined volume of space and intense heat is produced. What happens to gases at very high temperatures?

31. Changes of State
Changes in state occur with changes in kinetic energy

32. Gases, Liquids, and Solids cont’d
The beaker contains iodine crystals.
(b) Iodine has an appreciable vapor pressure even below its melting point.
Fig. 7.15

33. Evaporation of Liquids
Process by which molecules _____________ from the liquid phase to the _______ phase
In order for molecules in the _________ phase to change into molecules in the __________ phase, the molecules must ______ __________
__________ is gained through collisions with other molecules
Some molecules in a liquid have more energy than others
It is easier for surface molecules to escape than molecules in the middle of the liquid (because they are subjected to fewer attractive forces)
Rate of evaporation ______________ with temperature
The average ______________ energy of the molecules increases

34. Vapor Pressure in a Closed Container
Liquid and vapor in a closed container eventually reach equilibrium
A condition in which two opposite processes take place at the same rate
In this case, the two processes are evaporation and condensation
The vapor above the liquid in a closed container exerts vapor pressure
The pressure exerted by a vapor above a liquid when the liquid and vapor are in equilibrium with each other

35. Gases, Liquids, and Solids cont’d
Fig. 7.17
(a) the liquid level drops for a time, (b) then becomes constant. At that point a state of equilibrium has been reached in which (c) the rate of evaporation equals the rate of condensations.

36. Volatility
Substances with _________ vapor pressures evaporate _________
They are the substances with _________ attractive forces between molecules
Volatile substance:
A substance that readily evaporates at room temperature because of a high vapor pressure

37. Boiling and Boiling Point
A form of evaporation where conversion from the liquid state to the vapor state occurs within the body of the liquid through bubble formation
Boiling Point
The temperature at which the vapor pressure of a liquid becomes equal to the external (atmospheric) pressure exerted on the liquid
Normal boiling point: boiling point at 1 atm

38. Conditions Affecting Boiling Point
Boiling Point is increased by increasing the external pressure
Pressure cooker
Boiling Point is decreased by decreasing the external pressure
Boiling point at higher elevations is lower than at sea level

39. Table 7.3 Boiling Point of Water at Various Locations That Differ in Elevation.

40. Gases, Liquids, and Solids cont’d
Same principle applies to a pressurized automobile cooling system.

41. Intramolecular v. Intermolecular Forces
The covalent bond holding a molecule together is an intramolecular force.
The attraction between molecules is an intermolecular force.
Intermolecular forces are much weaker than intramolecular forces (e.g. 16 kJ/mol vs. 431 kJ/mol for HCl).
When a substance melts or boils the intermolecular forces are broken (not the covalent bonds).

42. Strength of Bonds

43. Intermolecular Forces
There are different intermolecular forces
_________ - ___________ Forces
_____________ “Bonds”
London ______________ Forces
Most of these interactions are driven by one general idea: opposite charges attract!

44. Dipole-Dipole Interactions
Attraction between polar molecules

45. Hydrogen Bonds
Unusually strong dipole-dipole interactions that occur between molecules with H-N, H-O, or H-F covalent bonds and a lone pair of electrons on another small, electronegative atom (N, O, or F).

46. Figure Diagrams of hydrogen bonding involving selected simple molecules. The solid lines represent covalent bonds; the dotted lines represent hydrogen bonds.

48. Figure If there were no hydrogen bonding between water molecules, the boiling point of water would be approximately - 80C.

49. London Dispersion Forces
Formed between adjacent neutral molecules
The nucleus of one molecule (or atom) attracts the electrons of the adjacent molecule (or atom).
For an instant, the electron clouds become distorted.
In that instant a dipole is formed (called an instantaneous dipole).
One instantaneous dipole can induce another instantaneous dipole in an adjacent molecule (or atom).

50. London Dispersion Forces, II
Polarizability is the ease with which an electron cloud can be deformed.
The larger the molecule (the greater the number of electrons) the more polarizable.
London dispersion forces ____________ as molecular weight ________________.
London dispersion forces exist between all molecules.
London dispersion forces depend on the shape of the molecule.

51. Gases, Liquids, and Solids cont’d
Fig. 7.24
Nonpolar molecules can develop instantaneous dipoles and induced dipoles.

52. Boiling Points of Nonpolar Substances

54. Relative Strengths of Interactions
Intramolecular Bonds:
Ionic Bonds  Strongest
Covalent Bonds  Weakest
Intermolecular Forces
Hydrogen “Bonds”  Strongest
Dipole-Dipole Forces
London Dispersion Forces  Weakest
The stronger the forces/attractions, the more energy that must be added to break the attractions (the higher the melting point and the higher the boiling point).

55. Question!
Which of the following molecules will not form hydrogen bonds?

56. Question!
Which forces would you expect to find in samples of the following molecules?
A. C3H8 (propane)
B. H2O
C. CH3F

57. Question!
Which of the following compounds would you expect to have the lowest boiling point?
A. C3H8 (propane)
B. H2O
C. CH3F

58. Question!
Which of the following compounds would you expect to have the highest boiling point?
A. C2H6
B. C3H8
C. C4H10
D. C5H12
Why?