1. Gases, Liquids, and Solids
Chapter 8 Lecture
Fundamentals of General, Organic, and Biological Chemistry
7th Edition
McMurry, Ballantine, Hoeger, Peterson
Chapter Eight
Gases, Liquids, and Solids
Julie Klare
Gwinnett Technical College
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2. 8.2 Intermolecular Forces
Intra- vs. inter-
(within) (between)

3. Liquids and Solids
There are two major types of intermolecular forces (IMF) in liquids and solids:
dipole–dipole forces – polar substances
Permanent dipole–dipole attractions
Relatively strong type of IMF
Hydrogen bonding is especially strong and biologically crucial
London dispersion forces – nonpolar substances
Temporary or “fleeting” charge imbalances
Relatively weak type of IMF
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4. (Permanent) Dipole-Dipole Forces
Dipole moment: property of a molecule with permanent positive & negative charge centers
Dipoles occur in polar molecules
The positive and negative ends of different polar molecules are permanently attracted to one another in condensed phases

5. Water is polar because it has a very large dipole moment
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6. The resulting balance of forces
Individual dipole-dipole forces are much weaker than ‘true’ covalent bonds (intramolecular forces)
Effects of many dipole–dipole forces are immense
That’s why polar molecules have high boiling points

7. nonpolar: No permanent IMFs polar: molecules attract permanently
bp = −0.5oC
bp = +56.2oC
nonpolar:
No permanent IMFs
polar:
molecules attract
permanently
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8. Hydrogen Bonding Very strong (permanent) dipole-dipole attraction
First, think of water
2 negative poles (d-) – the lone pairs
2 positive poles (d+) – H bonded to electronegative O
Explains why water is a great polar solvent
Each water molecule makes 4 hydrogen bonds…

9. Hydrogen bonding for non-water molecules
Typically, an attraction between H+ and OH-
-think of water as (H-OH)
Formally, an attraction between a hydrogen atom which is bonded to an O, N, or F atom… wth any nearby O, N, or F atoms

10. focus on ethanol alone can two ethanol molecules
hydrogen bond to each other?

11. focus on ethanol alone can two ethanol molecules
hydrogen bond to each other? YES

12. focus on dimethyl ether alone
can two dimethyl ether molecules
hydrogen bond to each other? NO
because there are no O-H bonds
(and of course, no N-H or F-H bonds)

13. Can ethanol hydrogen bond with dimethyl ether. Yes
Can ethanol hydrogen bond with dimethyl ether? Yes! There are two oxygens present, and one is an O-H

14. Because there are N-H bonds present
nitrogen
can two ammonia molecules
hydrogen bond to each other
YES
Because there are N-H bonds present

15. nitrogen can two trimethyl amine molecules
hydrogen bond to each other? NO
because there are no N-H bonds

16. nitrogen and oxygen together
Can trimethyl amine
hydrogen bond to ethanol?
YES
because there is an O-H bond

17. Can ammonia hydrogen bond to dimethyl ether
Can ammonia hydrogen bond to dimethyl ether? YES Because there is an N-H present

18. Effects of hydrogen bonding
Hydrogen bonding affects physical properties
Boiling point
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20. Concept Check
Below are two Lewis structures for the formula C2H6O How would their boiling points differ?
One Lewis structure could be ethanol and one Lewis structure could be dimethyl ether. Ethanol will have a higher boiling point than dimethyl ether because ethanol exhibits hydrogen bonding and dimethyl ether exhibits dipole-dipole interactions. Hydrogen bonding is an especially strong type of dipole-dipole interaction and will thus raise the boiling point of ethanol.
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21. Shown below is a model of liquid water
Shown below is a model of liquid water. What is the major intermolecular force of attraction responsible for water being a liquid?
Covalent bonding
Dipole–dipole
Hydrogen bonding
London dispersion
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22. Which of the following is not capable of hydrogen bonding?HF
H2O
NH3
CH4
Methane has H atoms, but none of
them are connected to an O, N, or F
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23. London Dispersion Force
How non-polar molecules condense

24. Nonpolar molecules are only really nonpolar on average (over time)
At any instant, however, fleeting charge imbalances occur
The electrons are constantly moving
Occasionally, more end up at one side of molecule
Higher molecular weight (more electrons) and surface area favor more London forces
An instantaneous charge distribution with electrons shifted to the left (d-). They would also shift right just as often (not shown).
Time-averaged charge distribution is uniform, as in the non-polar (symmetric) Lewis structure
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25. Concept Check Consider the following compounds: NH3 CH4 H2
How many of the compounds above exhibit London dispersion forces?
a) 0
b) 1
c) 2
d) 3
The correct answer is d. All molecules, whether nonpolar or polar, exhibit London dispersion forces.
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26. fyi: Grease Molecule lots of electrons lots of molecular surface area
so there are numerous London ‘sites’
resulting in a semi-solid at room temperature

27. fyi: Hexane Molecule fewer electrons
very little molecular surface area
resulting in fewer London sites
resulting in a liquid at room temperature

28. Like dissolves Like
London forces allow nonpolar molecules to “stick” together as liquids or solids
Permanent dipoles, especially hydrogen bonds, allow polar molecules to “stick”
Polar molecules do also experience London forces, but they are much weaker and irrelevent
Nonpolar and polar substances will not “stick” to each other
Oil (nonpolar) and water (polar) don’t mix

29. fyi
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30. 8.3 Gases and the Kinetic Molecular Theory
An ideal gas obeys all the assumptions of the kinetic–molecular theory 1. The ideal gas consists of hypothetical particles moving perfectly at random with zero attractive forces between them 2. The volume of the ideal gas particle is insignificant compared with the volume of its container – a gas is mostly empty space 3. The average kinetic energy of ideal gas particles is proportional to the Kelvin temperature 4. All collisions are perfectly elastic. Gasses exert pressure.
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31. Postulates of the Kinetic Molecular Theory
1. The ideal gas consists of particles moving perfectly at random with no attractive forces between them
IMF = intermolecular force

32. Postulates of the Kinetic Molecular Theory
2. The volume of the ideal gas particle is insignificant compared with the volume of its container
Solid and liquid particles are closely packed by touching each other.
A gas is mostly empty space. The particles do not touch, except when colliding, upon which they bounce (elasticity).
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33. Postulates of the Kinetic Molecular Theory
3. The average kinetic energy of ideal gas particles is proportional to the Kelvin temperature
Volume will increase with temperature as gas speeds up
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34. Postulates of the Kinetic Molecular Theory
4. All collisions of ideal gas particles are perfectly elastic in other words…
the total kinetic energy of a pair of colliding particles is unchanged following impact
collisions with
other particles or with
the container create a constant
pressure force equal in all directions
Higher T  faster collisions  higher P
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35. Concept Check
Which gas would behave more ideally at the same conditions of P and T? CO or N2 Why?
N2 would behave more ideally because it is nonpolar and only exhibits London dispersion forces, therefore the intermolecular forces between N2 molecules are weak (and thus the collisions will be more “elastic”). CO also exhibits dipole-dipole interactions.
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36. 8.4 Pressure = 𝑁𝑒𝑤𝑡𝑜𝑛𝑠 𝑚 2 or Pascals (Pa)
Gasses exert pressure forces uniformly in 3D space
Gasses exert this same pressure force on the 2D surface of a container or wall
English unit is pounds (of force) per square inch, or psi

37. Atmospheric (air) pressure
Gravity ‘pulls down’ on the
gas envelope surrounding our
planet, creating pressure
at the surface
= 14.7 pounds per square inch
= 101,325 Pascals
= 1 atmosphere
= 760 mm Hg
= 760 Torr
= psi (English unit)
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38. Simple barometer
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39. Simple manometer
Gas pressure in a container is measured using a manometer
The difference between the mercury levels indicates the difference between gas pressure and atmospheric pressure
Pressure is given in the SI system by the pascal (Pa)
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40. Conversions 1 atm = 760. mm Hg 1 mm Hg = 1 torr
we will frequently use: 1 atm = 760. mm Hg
for conversions
1 mm Hg = 1 torr

41. Oxygen gas is contained in the apparatus shown below
Oxygen gas is contained in the apparatus shown below. What is the pressure of the oxygen in the apparatus?
500 mm Hg
725 mm Hg
775 mm Hg
1000 mm Hg
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42. The Gas Laws All gas laws can be formulated with four variables Volume
Pressure
Temperature (Kelvins only!)
n (number of moles of gas)

43. 8.5 Boyle’s Law:
Boyle’s law:  The volume of a gas at constant temperature decreases proportionally as its pressure increases
Smaller V  more collisions with wall  higher P
e.g. double the pressure, half the volume
P1V1 = P2V2
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44. The volume of a balloon is 2. 85 L at a pressure of 763 mm Hg
The volume of a balloon is 2.85 L at a pressure of 763 mm Hg. What will the volume of the balloon be when the pressure is decreased to 755 mm Hg at a constant temperature?
2.82 L
0.355 L
2.88 L
0.347 L
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45. 8.6 Charles’s Law: The Relation between Volume and Temperature
Charles’s law:  The volume of a gas at constant pressure is directly proportional to its Kelvin temperature.
This is a proportional relationship, unlike the inverse relationship between P and V in Boyle’s Law.
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46. 8.7 Gay-Lussac’s Law:
Gay-Lussac’s law: The pressure of a gas at constant volume is directly proportional to its Kelvin temperature
As temperature goes up or down, pressure also goes up or down
Proportional relation between P and T
Higher T  more energetic collisions  higher P
It’s just a combination of Boyle’s and Charles’ Laws
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47. 8.8 The Combined Gas Law
Where the temperature remains constant, this equation ‘reduces’ to Boyle’s law
Where pressure is constant, it reduces to Charles’ law
Where volume is constant, it reduces to Gay-Lussac’s law

48. A hot-air balloon has a volume of 960 L at 291 K
A hot-air balloon has a volume of 960 L at 291 K. The balloon is heated up and the volume increases to 1070 L. What is the final temperature (in °C) of the balloon?
50 °C
80 °C
110 °C
130 °C
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49. More moles of gas  more volume
8.9 Avogadro’s Law
Avogadro’s law: the volume of a gas is directly proportional to its molar amount
at a constant pressure and temperature
More moles of gas  more volume
Total moles of any gas, possibly combined species!!!
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50. 1.0 mol of gas at 25 °C and 0.90 atm is contained in an apparatus with a movable piston. Which set of conditions will result in a lower piston position than shown in this drawing?
1.0 mol of gas, 25 °C, and 1.80 atm
1.0 mol of gas, 50 °C, and 0.90 atm
2.0 mol of gas, 25 °C, and 0.45 atm
2.0 mol of gas, 25 °C, and 0.90 atm
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51. If all other variables are held constant, which change will NOT cause a change in the pressure of oxygen in a mixture of oxygen and nitrogen?
Decreasing the moles of oxygen
Decreasing the temperature
Increasing moles of nitrogen
Increasing the volume
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52. At a constant volume, a flask is filled with helium at 25 °C and 1
At a constant volume, a flask is filled with helium at 25 °C and 1.03 atm pressure, sealed, and then heated to 98 °C. What is the pressure inside the flask?
0.827 atm
1.21 atm
1.28 atm
0.916 atm
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53. 8.10 The Ideal Gas Law: PV = nRT
The ideal gas law defines a standard state
STP = standard temperature and pressure
0 C ( K exactly)
1 atm (760 mmHg by definition)
The “standard volume” of 1 mole of (any) gas at STP is the same.
Standard volume for any gas at STP = L
R is the Universal Gas Constant
It’s units must match the pressure and volume units
R = L•atm/mol•K = L•mm Hg/mol•K = …
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54. At STP, 22.414 L of an ideal gas would just fit into this precision ball
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55. Which of the following condition(s) are NOT considered to be standard temperature or pressure?
760 mm Hg
755 torr
0 °C
Both a and b
None of the above
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56. What is the volume of 3.86 g of nitrogen gas at STP?
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57. 8.11 Partial Pressure and Dalton’s Law
Each particle in a gas acts independently,
so its identity becomes irrelevant.
Thus, gas pressures add…
just like liquid volumes.
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58. Partial pressures add to the total pressure.
Mixtures of gases behave the same as a single pure gas and obey the same laws
Dry air is a mixture of 21% O2, 78% N2, and 1% Ar by volume (and by mole percent)
Partial pressure is the contribution of each gas in a mixture to the total pressure (P).
Proportional to volume (and mole percent)
e.g. for air at STP (P = 1 atm), partial pressures are
0.21 atm for O2 ( = 21% of 1 atm total pressure)
0.78 atm for N2
0.01 atm for Ar
Partial pressures add to the total pressure.
P = P1 + P2 + P3 + …
Above partial pressures for O2, N2 and Ar add to 1 atm
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59. So for a mixture of ideal gases, it is the total number of ‘particles’ that is important
Not the identity or composition of the involved gases + 
2 atm gas A
5 atm gas B
7 atm total in the mixture

60. Exercise Calculate the new partial pressure of oxygen 6.13 atm
27.4 L of oxygen gas at 25.0°C and 1.30 atm, and 8.50 L of helium gas at 25.0°C and 2.00 atm were pumped into a tank with a volume of 5.81 L at 25.0°C.
Calculate the new partial pressure of oxygen
6.13 atm
Calculate the new partial pressure of helium
2.93 atm
Calculate the new total pressure of both
9.06 atm
For oxygen:
P1V1=P2V2
(1.30 atm)(27.4 L) = (P2)(5.81 L)
P2 = 6.13 atm
For helium:
(2.00 atm)(8.50 L) = (P2)(5.81 L)
P2 = 2.93 atm
The total pressure is therefore = 9.06 atm.

61. 8.12 Liquids Liquids are usually in equilibrium with their vapor (gas)
Some molecules have higher than average energy and “escape” through the liquid-vapor surface into gas form
Dynamic equilibrium is reached. Evaporation and condensation occur constantly and at the same rate.
Thus liquids exhibit a constant vapor pressure.
It increases with T (higher average energy)
Liquid in initially evacuated flask (no pressure).
Liquid starts evaporating.
Evaporation and condensation reach equilibrium. The gas exerts vapor pressure over the liquid.
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62. Definition
Normal boiling point is the boiling point under a pressure of exactly 1 atmosphere
A liquid’s vapor pressure (and thus b.p.) depends on temperature, atmospheric pressure, and the chemical properties of the liquid itself … eg, is it polar?

63. All other things being equal, polar molecules have lower vapor pressures, and thus higher boiling points

64. Viscosity
Many familiar properties of liquids can be understood by studying intermolecular forces
Viscosity
some liquids flow easily like gasoline, and some are sluggish like honey
The measure of a liquid’s resistance to flow is called viscosity
Viscosity increases with increasing intermolecular forces

65. Which would you expect to be more viscous?
nonpolar
polar
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66. This explains why gravity can make a puddle grow only just so large
Surface tension is caused by the difference between the intermolecular forces experienced by molecules at the surface of the liquid and those experienced by molecules in the interior. P239
Liquid molecules exert more IMFs with each other than the surrounding gas. The liquid surface pulls inward.
This explains why gravity can make a puddle grow only just so large
Substances with high surface tension ‘bead up’
Substances with low surface tension spread out thin
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67. 8.13 Water: A Unique Liquid
Liquid water is denser than solid water (ice) – so ice floats on water
Typically, a solid is denser than its liquid is denser than its gas
The unique, extremely strong hydrogen bonding pulls the liquid water molecules close together
Closer than the lattice distance between the ice molecules in an ice crystal, which has a regular spacing of the molecules
Ice molecules are frozen in place, and hydrogen bonding cannot pull them closer together as for the liquid
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68. 8.14 Solids
Metallic solids can be viewed as vast three-dimensional arrays of metal cations immersed in a sea of electrons.
The electron sea acts as a glue to hold the cations together and as a mobile carrier of charge to conduct electricity.
Bonding attractions extend uniformly in all directions, so metals are malleable (bendable) rather than brittle. When a metal crystal receives a sharp blow, the electron sea adjusts to the new distribution of cations.
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69. FYI
An amorphous solid is one whose constituent particles are randomly arranged and have no ordered long-range structure
It’s an extremely viscous liquid that appears like a solid
Amorphous solids often result when liquids cool before they can achieve internal order (glass), or when their molecules are large and tangled together (viscosity modifiers in motor oil)
Glass, tar, opal, and some hard candies are amorphous solids
Glass is really a liquid… in many thousand years it will form a puddle.
Compare amorphous (technically liquid) glass to the solid phase crystal. Crystal is much more brittle.
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70. 8.15 Changes of State
Heats of melting and boiling are technically called latent heats of fusion and vaporization, respectively. They are measured in units of J/mol or cal/mol. Latent means hidden, meaning that no temperature change is “sensed” during fusion or vaporization.

71. Vaporization requires considerably more energy than melting… must overcome IMFs to separate the liquid molecules into gas ΔHvap water = 540. cal per gram ΔHvap water = cal per mole

72. What is the boiling point of the substance having the heating curve shown below?
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73. If intermolecular forces are strong then large amounts of heat must be added to overcome them
so latent heats are large
so boiling points and freezing points are high
Volatile substances have low IMFs, high vapor pressure, and low boiling points
Typically nonpolar organic compounds
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74. What is the relationship between intermolecular forces (IMF) and the boiling point of a liquid?
As IMF increase, boiling point increases.
As IMF increase, boiling point does not change.
As IMF increase, boiling point decreases.
None of the above
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