Chapter Eight Gases, Liquids, and Solids Fundamentals of General, Organic, and Biological Chemistry 5th Edition James E. Mayhugh Oklahoma City University  2007 Prentice Hall, Inc.

Prentice Hall © 2007 Chapter Eight 2 Outline ► 8.1 States of Matter and Their Changes ► 8.2 Gases and the Kinetic–Molecular Theory ► 8.3 Pressure ► 8.4 Boyle’s Law: The Relation Between Volume and Pressure ► 8.5 Charles’s Law: The Relation Between Volume and Temperature ► 8.6 Gay-Lussac’s Law: The Relation Between Pressure and Temperature ► 8.7 The Combined Gas Law ► 8.8 Avogadro’s Law: The Relation Between Volume and Molar Amount ► 8.9 The Ideal Gas Law ► 8.10 Partial Pressure and Dalton’s Law ► 8.11 Intermolecular Forces ► 8.12 Liquids ► 8.13 Water: A Unique Liquid ► 8.14 Solids ► 8.15 Changes of State

Prentice Hall © 2007 Chapter Eight States of Matter and Their Changes attractive forces ► Matter exists in any of three phases, or states—solid, liquid, and gas, depending on the attractive forces between particles, and temperature, and pressure. ► Review Ch 5.9, polarity very weak ► In a gas, the attractive forces between particles are very weak compared to their kinetic energy, so the particles move about freely, are far apart, and have almost no influence on one another.

Prentice Hall © 2007 Chapter Eight 4 stronger ► In a liquid, the attractive forces between particles are stronger, pulling the particles close together but still allowing them considerable freedom to move about. much stronger ► In a solid, the attractive forces are much stronger than the kinetic energy of the particles, so the atoms, molecules, or ions are held in a specific arrangement and can only wiggle around in place.

Prentice Hall © 2007 Chapter Eight 5 ► Phase change or change of state: The transformation of a substance from one state to another. ► Melting point (mp): The temperature at which solid and liquid are in equilibrium. ► Boiling point (bp): The temperature at which liquid and gas are in equilibrium. ► Sublimation: A process in which a solid changes directly to a gas.

Prentice Hall © 2007 Chapter Eight 6 Melting, boiling, and sublimation all have  H > 0, and  S > 0. This means they are nonspontaneous, below and spontaneous above a certain temperature.

Prentice Hall © 2007 Chapter Eight 7 When isopropyl alcohol, (CH 3 ) 2 CHOH vaporizes, what are the signs of  H and  S for the vaporization process?  H = – and  S = –  H = – and  S =  H = + and  S = –  H = + and  S = +

Prentice Hall © 2007 Chapter Eight 8 When isopropyl alcohol, (CH 3 ) 2 CHOH vaporizes, what are the signs of  H and  S for the vaporization process?  H = – and  S = –  H = – and  S =  H = + and  S = –  H = + and  S = +

Chapter Eight

Chapter Seven The figures below depict mercury in three different states. Identify the change of state occurring when mercury is taken from the state in figure (c) to the state in figure (b), and give the name of the quantity of energy involved. 1.Boiling, heat of vaporization 2.Dissolution, heat of solution 3.Melting, heat of fusion 4.Sublimation, heat of sublimation

Chapter Seven The figures below depict mercury in three different states. Identify the change of state occurring when mercury is taken from the state in figure (c) to the state in figure (b), and give the name of the quantity of energy involved. 1.Boiling, heat of vaporization 2.Dissolution, heat of solution 3.Melting, heat of fusion 4.Sublimation, heat of sublimation

Chapter Seven

Prentice Hall © 2007 Chapter Eight Gases and the Kinetic-Molecular Theory ► The behavior of gases can be explained by a group of assumptions known as the kinetic–molecular theory of gases. The following assumptions account for the observable properties of gases: ► A gas consists of many particles, either atoms or molecules, moving about at random with no attractive forces between them. Because of this random motion, different gases mix together quickly.

Prentice Hall © 2007 Chapter Eight 15 ► The amount of space occupied by the gas particles themselves is much smaller than the amount of space between particles. Most of the volume taken up by gases is empty space, accounting for the ease of compression and low densities of gases. ► The average kinetic energy of gas particles is proportional to the Kelvin temperature. Thus, gas particles have more kinetic energy and move faster as the temperature increases. (In fact, gas particles move much faster than you might suspect. The average speed of a helium atom at room temperature and atmospheric pressure is approximately 1.36 km/s, or 3000 mi/hr, nearly that of a rifle bullet, sound travels 760 mi/hr)

Prentice Hall © 2007 Chapter Eight 16 ► Collisions of gas particles, either with other particles or with the wall of their container, are elastic; that is, the total kinetic energy of the particles is constant. The pressure of a gas against the walls of its container is the result of collisions of the gas particles with the walls. The number and force of collisions determines the pressure. ► A gas that obeys all the assumptions of the kinetic– molecular theory is called an ideal gas. All gases behave somewhat differently than predicted by the kinetic–molecular theory at very high pressures or very low temperatures. Most real gases display nearly ideal behavior under normal conditions.

Prentice Hall © 2007 Chapter Eight Pressure ► Pressure (P) is defined as a force (F) per unit area (A) pushing against a surface; P = F/A. ► A barometer measures pressure as the height of a mercury column. Atmospheric pressure presses down on mercury in a dish and pushes it up a tube. ► Pressure units: 1 atm = 760 mm Hg = 14.7 psi = 101,325 Pa 1 mm Hg = 1 torr = Pa

A column of air weighing 14.7 lb presses down on each square inch of the Earth’s surface at sea level, resulting in what we call atmospheric pressure.

Prentice Hall © 2007 Chapter Eight 20 Gas pressure inside a container is often measured using an open-end manometer, a simple instrument similar in principle to the mercury barometer.

Chapter Seven

1.500 mm Hg mm Hg mm Hg mm Hg Oxygen gas is contained in the apparatus shown below. What is the pressure of the oxygen in the apparatus?

1.500 mm Hg mm Hg mm Hg mm Hg Oxygen gas is contained in the apparatus shown below. What is the pressure of the oxygen in the apparatus?

Prentice Hall © 2007 Chapter Eight Boyle’s Law: The Relation Between Volume and Pressure ► Boyle’s law: The volume of a gas is inversely proportional to its pressure for a fixed amount of gas at a constant temperature. That is, P times V is constant when the amount of gas n and the temperature T are kept constant. ► V  1/P or PV = k if n and T are constant ► If: P 1 V 1 = k and P 2 V 2 = k ► Then: P 1 V 1 = P 2 V 2

Prentice Hall © 2007 Chapter Eight 26 The volume of a gas decreases proportionately as its pressure increases. If the pressure of a gas sample is doubled, the volume is halved.

28 A sample of helium gas has a volume of 6.4 L at a pressure of 0.70 atm. What is the new volume when the pressure is increased to 1.40 atm (T constant)? A) 3.2 LB) 6.4 LC) 12.8 L Learning Check

29 A) 3.2 L Solve for V 2 : P 1 V 1 = P 2 V 2 V 2 = V 1 P 1 P 2 V 2 = 6.4 L x 0.70 atm = 3.2 L 1.40 atm Volume decreases when there is an increase in the pressure (Temperature is constant). Solution

Prentice Hall © 2007 Chapter Eight Charles’ Law: The Relation Between Volume and Temperature ► Charles’s law: The volume of a gas is directly proportional to its Kelvin temperature for a fixed amount of gas at a constant pressure. That is, V divided by T is constant when n and P are held constant. ► V  T or V/T = k if n and P are constant ► If: V 1 /T 1 = k and V 2 /T 2 = k ► Then: V 1 /T 1 = V 2 /T 2

Prentice Hall © 2007 Chapter Eight 31

Prentice Hall © 2007 Chapter Eight 33 If the Kelvin temperature of a gas is doubled, its volume doubles.

Assume you have a sample of gas at 350K in a sealed container, as represented in part (a). Which drawing (b) - (d) represents the gas after the temperature is lowered to 150K? Using Charles’s law you should note that the volume would decrease with decreasing temperature

35 Learning Check Solve Charles’ Law expression for T 2. V 1 = V 2 T 1 T 2 T 2 =V 2 T 1 V 1

36 A balloon has a volume of 785 mL at 21°C. If The temperature drops to 0°C, what is the new volume of the balloon (P constant)? 1.Set up data table: Conditions 1Conditions 2 V 1 = 785 mLV 2 = ? T 1 = 21°C = 294 KT 2 = 0°C = 273 K Be sure that you always use the Kelvin (K) temperature in gas calculations. Learning Check

37 Learning Check 2. Solve Charles’ law for V 2 V 1 = V 2 T 1 T 2 V 2 = V 1 T 2 T 1 V 2 = 785 mL x 273 K = 729 mL 294 K

Prentice Hall © 2007 Chapter Eight Gay-Lussac’s Law: The Relation Between Pressure and Temperature ► Gay-Lussac’s law: The pressure of a gas is directly proportional to its Kelvin temperature for a fixed amount of gas at a constant volume. That is, P divided by T is constant when n and V are held constant. ► P  T or P/T = k if n and V are constant ► If: P 1 /T 1 = k and P 2 /T 2 = k ► Then: P 1 /T 1 = P 2 /T 2

Prentice Hall © 2007 Chapter Eight 39 As the temperature goes up, the pressure also goes up.

40 A gas has a pressure at 2.0 atm at 18°C. What is the new pressure when the temperature is 62°C? (V and n constant) 1. Set up a data table. Conditions 1Conditions 2 P 1 = 2.0 atmP 2 = T 1 = 18°C T 2 = 62°C = 291 K = 335 K Calculation with Gay-Lussac’s Law ?

41 Calculation with Gay-Lussac’s Law (continued) 2. Solve Gay-Lussac’s Law for P 2 P 1 = P 2 T 1 T 2 P 2 = P 1 T 2 T 1 P 2 = 2.0 atm x 335 K = 2.3 atm 291 K

42 Use the gas laws to complete with 1) Increases 2) Decreases A. Pressure _______ when V decreases. B. When T decreases, V _______. C. Pressure _______ when V changes from 12.0 L to 24.0 L. D. Volume _______ when T changes from 15.0 °C to 45.0°C. Learning Check Increases decreases increases

Prentice Hall © 2007 Chapter Eight The Combined Gas Law ► Since PV, V/T, and P/T all have constant values for a fixed amount of gas, these relationships can be merged into a combined gas law for a fixed amount of gas. ► Combined gas law: PV/T = k if n constant ► P 1 V 1 /T 1 = P 2 V 2 /T 2 ► If any five of the six quantities in this equation are known, the sixth can be calculated.

44 A sample of helium gas has a volume of L, a pressure of atm and a temperature of 29°C. At what temperature (°C) will the helium have a volume of 90.0 mL and a pressure of 3.20 atm (n constant)? 1. Set up Data Table Conditions 1Conditions 2 P 1 = atm P 2 = 3.20 atm V 1 = L (180 mL) V 2 = 90.0 mL T 1 = 29°C = 302 KT 2 = ?? Learning Check

45 2. Solve for T 2 P 1 V 1 =P 2 V 2 T 1 T 2 T 2 = T 1 P 2 V 2 P 1 V 1 T 2 = 302 K x 3.20 atm x 90.0 mL = 604 K atm mL T 2 = 604 K – 273 = 331 °C Learning Check

46 A gas has a volume of 675 mL at 35°C and atm pressure. What is the volume(mL) of the gas at –95°C and a pressure of 802 mm Hg (n constant)? Learning Check

47 Data Table T 1 = 308 KT 2 = -95°C = 178K V 1 = 675 mL V 2 = ??? P 1 = 646 mm Hg P 2 = 802 mm Hg Solve for T 2 V 2 =V 1 P 1 T 2 P 2 T 1 V 2 = 675 mL x 646 mm Hg x 178K = 314 mL 802 mm Hg x 308K Learning Check

Prentice Hall © 2007 Chapter Eight Avogadro’s Law: The Relation Between Volume and Molar Amount ► Avogadro’s law: The volume of a gas is directly proportional to its molar amount at a constant pressure and temperature. That is, V divided by n is constant when P and T are held constant. ► V  n or V/n = k if P and T are constant ► If: V 1 /n 1 = k and V 2 /n 2 = k ► Then: V 1 /n 1 = V 2 /n 2

Prentice Hall © 2007 Chapter Eight 49 ► The molar amounts of any two gases with the same volume are the same at a given T and P. ► Standard temperature and pressure: (STP) = 0  C ( K) and 1 atm (760 mm Hg) ► Standard molar volume of a gas at STP = 22.4 L/mol

Prentice Hall © 2007 Chapter Eight 50 ► Avogadro’s law. Each of these 22.4 L bulbs contains 1.00 mol of gas at 0 degrees C and 1 atm pressure. ► Equal volumes of gases contain equal numbers of moles, regardless of the identity of the gas. Under standard temperature and pressure, 1.00 mole of any gas will occupy 22.4 liters.

Prentice Hall © 2007 Chapter Eight The Ideal Gas Law ► Ideal gas law: The relationships among the four variables P, V, T, and n for gases can be combined into a single expression called the ideal gas law. ► PV/nT = R (A constant value) or PV = nRT ► If the values of three of the four variables in the ideal gas law are known, the fourth can be calculated. ► Values of the gas constant R: For P in atm: R = L·atm/mol·K For P in mm Hg: R = 62.4 L·mm Hg/mol·K

Prentice Hall © 2007 Chapter Eight 52

Prentice Hall © 2007 Chapter Eight Partial Pressure and Dalton’s law ► Dalton’s law: The total pressure exerted by a gas mixture of (P total ) is the sum of the partial pressures of the components in the mixture. ► Dalton’s law P total = P gas1 + P gas2 + P gas3 + … ► Partial pressure: The contribution of a given gas in a mixture to the total pressure.

Chapter Seven

Prentice Hall © 2007 Chapter Eight Intermolecular Forces ► Intermolecular force: A force that acts between molecules and holds molecules close to one another. There are three major types of intermolecular forces. ► Dipole–dipole forces are weak, with strengths on the order of 1 kcal/mol ► London dispersion forces are weak, in the range 0.5–2.5 kcal/mol. They increase with molecular weight and molecular surface area. ► Hydrogen bonds can be quite strong, with energies up to 10 kcal/mol.

Prentice Hall © 2007 Chapter Eight 56 Dipole–dipole forces: The positive and negative ends of polar molecules are attracted to one another by dipole–dipole forces. As a result, polar molecules have higher boiling points than nonpolar molecules of similar size.

Prentice Hall © 2007 Chapter Eight 57 ► Only polar molecules experience dipole–dipole forces, but all molecules, regardless of structure, experience London dispersion forces. ► (a) On average, the electron distribution in a nonpolar molecule is symmetrical. (b) At any instant, it may be unsymmetrical, resulting in a temporary polarity that can attract neighboring molecules.

Prentice Hall © 2007 Chapter Eight 60 A hydrogen bond is an attractive interaction between an unshared electron pair on an electronegative O, N, or F atom and a positively polarized hydrogen atom bonded to another electronegative O, N, or F. Hydrogen bonds occur in both water and ammonia.

Prentice Hall © 2007 Chapter Eight 61 The boiling points of NH 3, H 2 O, and HF are much higher than the boiling points of their second row neighbor CH 4 and of related third-row compounds due to hydrogen bonding.

Chapter Seven

1.Covalent bonding 2.Dipole-dipole 3.Hydrogen bonding 4.London dispersion Shown below is a model of liquid water. What is the major intermolecular force of attraction responsible for water being a liquid?

1.Covalent bonding 2.Dipole-dipole 3.Hydrogen bonding 4.London dispersion Shown below is a model of liquid water. What is the major intermolecular force of attraction responsible for water being a liquid?

Which of the following compounds form hydrogen bonds? Methyl alcohol and methylamine both have hydrogen attached to a very polar atom (oxygen, nitrogen) so they may form hydrogen bonds.

Prentice Hall © 2007 Chapter Eight Liquids ► Molecules are in constant motion in the liquid state. If a molecule happens to be near the surface of a liquid, and if it has enough energy, it can break free of the liquid and escape into a state called vapor. ► Once molecules have escaped from the liquid into the gas state, they are subject to all the gas laws. The gas molecules make their own contribution to the total pressure of the gas above the liquid according to Dalton’s law. We call this contribution the vapor pressure of the liquid.

Prentice Hall © 2007 Chapter Eight 67 ► Vapor pressure rises with increasing temperature until ultimately it becomes equal to the pressure of the atmosphere. At this point, bubbles of vapor form under the surface and force their way to the top; this is called boiling. ► At a pressure of exactly 760 mm Hg, boiling occurs at what is called the normal boiling point. ► If atmospheric pressure is higher or lower than normal, the boiling point of a liquid changes accordingly. At high altitudes, for example, atmospheric pressure is lower than at sea level, and boiling points are also lower.

Prentice Hall © 2007 Chapter Eight 68 At a liquid’s boiling point, its vapor pressure is equal to atmospheric pressure. Commonly reported boiling points are those at 760 mm Hg.

Prentice Hall © 2007 Chapter Eight 69 ► Surface tension: the resistance of a liquid to spread out and increase its surface area. The beading-up of water on a newly waxed car is due to surface tension. ► Surface tension is caused by the difference between the forces experienced by molecules at the surface and those experienced by molecules in the interior.

Prentice Hall © 2007 Chapter Eight Water: A Unique Liquid ► Water covers nearly 71% of the Earth’s surface, it accounts for 66% of the mass of an adult human body, and it is needed by all living things. ► Water has the highest specific heat of any liquid, giving it the capacity to absorb a large quantity of heat while changing only slightly in temperature. ► As a result, large lakes and other bodies of water tend to moderate the air temperature and the human body is better able to maintain a steady internal temperature under changing outside conditions.

Prentice Hall © 2007 Chapter Eight 71 ► Water has an unusually high heat of vaporization (540 cal/g), it carries away a large amount of heat when it evaporates. ► Your body relies on the cooling effect of water evaporation.

Prentice Hall © 2007 Chapter Eight 72 Most substances are more dense as solids than as liquids because molecules are more closely packed in the solid than in the liquid. Water, however, is different. Liquid water has a maximum density of g/mL at 3.98°C but then becomes less dense as it cools. When it freezes, its density decreases still further to g/mL. Ice floats on liquid water, and lakes and rivers freeze from the top down. If the reverse were true, fish would be killed in winter.

The large spaces that form when these crystals form cause ice to be less dense than liquid water. Therefore ice freezes on the surface of lakes in cold climates, insulating the water below and protecting aquatic life from extremely cold temperatures.

Prentice Hall © 2007 Chapter Eight Solids ► There are many different kinds of solids. The most fundamental distinction between solids is that some are crystalline and some are amorphous. ► Crystalline solid: A solid whose atoms, molecules, or ions are rigidly held in an ordered arrangement. Crystalline solids can be further categorized as ionic, molecular, covalent network, or metallic. ► Amorphous solid: A solid whose particles do not have an orderly arrangement.

Prentice Hall © 2007 Chapter Eight 75 A summary of the different types of solids and their characteristics is given below.

Prentice Hall © 2007 Chapter Eight Changes of State ► When a substance changes state, energy added is used to overcome attractive forces instead of increasing kinetic energy so temperature does not change. ► Heat of fusion: The quantity of heat required to completely melt a substance once it has reached its melting point. ► Heat of vaporization: The quantity of heat required to completely vaporize a substance once it has reached its boiling point.

Prentice Hall © 2007 Chapter Eight 77 A heating curve for water, showing the temperature and state changes that occur when heat is added.

1.–50 o C 2.12 o C 3.75 o C o C What is the boiling point of the substance having the heating curve shown below?

1.–50 o C 2.12 o C 3.75 o C o C What is the boiling point of the substance having the heating curve shown below?

Chapter Seven

Prentice Hall © 2007 Chapter Eight 81 Chapter Summary ► According to the kinetic–molecular theory of gases, the behavior of gases can be explained by assuming that they consist of particles moving rapidly at random, separated from other particles by great distances, and colliding without loss of energy. ► Boyle’s law says that the volume of a fixed amount of gas at constant temperature is inversely proportional to its pressure. ► Charles’s law says that the volume of a fixed amount of gas at constant pressure is directly proportional to its Kelvin temperature.

Prentice Hall © 2007 Chapter Eight 82 Chapter Summary Cont. ► Gay-Lussac’s law says that the pressure of a fixed amount of gas at constant volume is directly proportional to its Kelvin temperature. ► Avogadro’s law says that equal volumes of gases at the same temperature and pressure contain the same number of moles. ► The four gas laws together give the ideal gas law, PV = nRT, which relates the effects of temperature, pressure, volume, and molar amount. ► At 0°C and 1 atm pressure, called standard temperature and pressure (STP), 1 mol of any gas occupies a volume of 22.4 L.

Prentice Hall © 2007 Chapter Eight 83 Chapter Summary Cont. ► The pressure exerted by an individual gas in a mixture is called the partial pressure. Dalton’s law: the total pressure exerted by a mixture is equal to the sum of the partial pressures of the individual gases. ► There are three major types of intermolecular forces, which act to hold molecules near one another in solids and liquids. Dipole–dipole forces occur between polar molecules. London dispersion forces occur between all molecules as a result of temporary molecular polarities. Hydrogen bonding, the strongest of the three forces, occurs between a hydrogen atom bonded to O, N, or F and a nearby O, N, or F atom.

Prentice Hall © 2007 Chapter Eight 84 Chapter Summary Cont. ► Crystalline solids are those whose constituent particles have an ordered arrangement; amorphous solids lack internal order. There are several kinds of crystalline solids, ionic solids, molecular solids, covalent network solids, and metallic solids,. ► The amount of heat necessary to melt a given amount of solid at its melting point is its heat of fusion. Molecules escape from the surface of a liquid resulting in a vapor pressure of the liquid. At a liquid’s boiling point, its vapor pressure equals atmospheric pressure. The amount of heat necessary to vaporize a given amount of liquid at its boiling point is called its heat of vaporization.

Prentice Hall © 2007 Chapter Eight 85 End of Chapter 8