Gases Liquids and Solids The Phases or States

Gases, Liquids, and Solids The Phases, or States, of Matter Copyright © Houghton Mifflin Company. All rights reserved. 1

Physical States of Matter A solid has a definite shape and a definite volume. A liquid has an indefinite shape - it takes the shape of its container – a definite volume. A gas has an indefinite shape and an indefinite volume – it expands to fill its container. Copyright © Houghton Mifflin Company. All rights reserved. 2

Table 6. 1 Distinguishing Properties of Solids, Liquids, and Gases. Copyright © Houghton Mifflin Company. All rights reserved. 3

6. 1 The Kinetic Molecular Theory of Matter 1. Matter is composed of tiny particles. 2. The particles are in constant random motion and possess kinetic energy. 3. The particles interact with each other through attractions and repulsions and possess potential energy. Copyright © Houghton Mifflin Company. All rights reserved. 4

6. 1 The Kinetic Molecular Theory of Matter 4. The velocity of particles increases with temperature, as does their kinetic energy. 5. The particles transfer energy to each other through elastic collisions. Copyright © Houghton Mifflin Company. All rights reserved. 5

Figure 6. 2 Upon release, the steel ball on the left transmits kinetic energy through elastic collisions to the ball on the right. Copyright © Houghton Mifflin Company. All rights reserved. 6

6. 2 Kinetic Molecular Theory and Physical States In solids, cohesive forces (potential energy) dominate over disruptive forces (kinetic energy). In liquids, cohesive forces (potential energy) and disruptive forces (kinetic energy) are similar in magnitude. In gases, disruptive forces (kinetic energy) dominate over cohesive forces (potential energy). Copyright © Houghton Mifflin Company. All rights reserved. 7

(a) Particles in a solid (atoms, molecules, or ions) are close together and vibrate about fixed sites. (b) Particles in a liquid, though still close together, freely slide over one another. (c) Particles in a gas are in constant random motion, each particle being independent of the others present. Copyright © Houghton Mifflin Company. All rights reserved. 8

When a gas is compressed, the amount of empty space in the container is decreased. The size of the molecules does not change; they simply move closer together. Copyright © Houghton Mifflin Company. All rights reserved. 9

6. 3 Gas Law Variables Volume Expressed in milliliters or liters Temperature Expressed in K (°C + 273 = K) Amount Expressed in moles (n) Pressure (Force per unit area, F/A) Expressed in atmospheres, mm Hg, or torr Copyright © Houghton Mifflin Company. All rights reserved. 10

Figure 6. 5 The essential components of a mercury barometer are a graduated glass tube, a glass dish, and liquid mercury. Copyright © Houghton Mifflin Company. All rights reserved. 11

6. 4 Boyle’s Law: A Pressure-Volume Relationship Copyright © Houghton Mifflin Company. All rights reserved. 12

6. 4 Boyle’s Law: A Pressure-Volume Relationship P 1 x V 1 = P 2 x V 2 A sample of O 2 gas occupies 1. 50 L at a pressure of 735 mm Hg and a temperature of 25 C. What volume will it occupy if the pressure is increased to 770 mm Hg, and the temperature does not change? Copyright © Houghton Mifflin Company. All rights reserved. 13

Figure 6. 8 Filling a syringe with a liquid is an application of Boyle's law. Copyright © Houghton Mifflin Company. All rights reserved. 14

6. 5 Charles’ Law: A Temperature-Volume Relationship Copyright © Houghton Mifflin Company. All rights reserved. 15

6. 5 Charle’s Law: A Temperature-Volume Relationship _V 1_ = _V 2_ T 1 T 2 A sample of gaseous anaesthetic has a volume of 425 m. L at a temperature of 37 C. What is its volume if it is cooled to 20 C at constant pressure? Copyright © Houghton Mifflin Company. All rights reserved. 16

6. 6 The Combined Gas Law _P 1 V 1_ = T 1 _P 2 V 2_ T 2 A 1. 50 L sample of N 2 O gas at a pressure of 755 mm Hg has a temperature of O C. What volume will the gas occupy at 50 C and 725 mm Hg? Copyright © Houghton Mifflin Company. All rights reserved. 17

6. 7 The Ideal Gas Law The ideal gas law includes the quantity of gas, in moles. PV = n. RT R = 0. 0821 L • atm mol • K Copyright © Houghton Mifflin Company. All rights reserved. 18

6. 7 The Ideal Gas Law Carbon monoxide, CO, is a colorless, odorless, tasteless gas that forms from incomplete combustion of carbon compounds. What volume is occupied by 1. 52 moles of this gas at 0. 992 atm pressure, and 65 C? (IV-1) Copyright © Houghton Mifflin Company. All rights reserved. 19

6. 7 The Ideal Gas Law How many moles of gas are present in a flask that holds 100. 0 m. L, at the boiling point of water (100 C), and a pressure of 760 mm Hg? If the gas has a mass of 0. 750 g, what is its molar mass? Copyright © Houghton Mifflin Company. All rights reserved. 20

6. 8 Dalton’s Law of Partial Pressures In a mixture of gases, each gas behaves as if the others were not there, and exerts its own pressure. Copyright © Houghton Mifflin Company. All rights reserved. 21

6. 8 Dalton’s Law of Partial Pressures PTotal = P 1 + P 2 + P 3 + …. Air is a mixture of N 2, O 2, and small amounts of other gases, mostly water vapor. If the atmospheric pressure is 758 torr, the partial pressure of oxygen is 146 torr, and the partial pressure of nitrogen is 594 torr, what is the partial pressure of water vapor? Copyright © Houghton Mifflin Company. All rights reserved. 22

6. 9 Changes of State A process in which a substance is transformed from one physical state to another. Heating or Cooling Changing Pressure Copyright © Houghton Mifflin Company. All rights reserved. 23

Figure 6. 13 There are six changes of state possible for substances. Copyright © Houghton Mifflin Company. All rights reserved. 24

Figure 6. 14 Sublimation and deposition of iodine. (a) The beaker contains iodine crystals. (b) Iodine has an appreciable vapor pressure be low its melting point. When heated, the solid sublimes. The vapor deposits crystals on the cool surface. Source: James Scherer Copyright © Houghton Mifflin Company. All rights reserved. 25

6. 10 Evaporation of Liquids Evaporation is the process by which molecules escape from the liquid phase to the gas phase. Rate of evaporation is proportional to temperature. Evaporation isn't necessarily boiling. Vapor describes gaseous molecules of a substance that is mostly present as a liquid or a solid. Copyright © Houghton Mifflin Company. All rights reserved. 26

6. 11 The Vapor Pressures of Liquids In a closed container, a liquid evaporates until the vapor and liquid reach equilibrium. Rate of evaporation equals rate of condensation Vapor pressure of the liquid can be measured Vapor pressure varies with temperature Volatile substances have high vapor pressure Copyright © Houghton Mifflin Company. All rights reserved. 27

Evaporation of a liquid in a closed container (a) Liquid level drops for a time (b) Liquid level becomes constant (ceases to drop). (c) Equilibrium has been reached; Rate of evaporation equals rate of condensation. Liquid exerts characteristic vapor pressure Copyright © Houghton Mifflin Company. All rights reserved. 28

Table 6. 2 Vapor Pressure of Water at Various Temperatures. Copyright © Houghton Mifflin Company. All rights reserved. 29

6. 12 Boiling and Boiling Point Boiling is a form of evaporation that takes place throughout a liquid, and involves bubble formation Boiling occurs when a liquid's vapor pressure equals that of the external pressure Normal boiling point is the temperature at which a liquid boils at 760 mm Hg. Copyright © Houghton Mifflin Company. All rights reserved. 30

Figure 6. 16 Bubbles of vapor form within a liquid when the temperature of the liquid reaches the liquid's boiling point. Copyright © Houghton Mifflin Company. All rights reserved. 31

Table 6. 3 Boiling Point of Water at Various Locations That Differ in Elevation. Copyright © Houghton Mifflin Company. All rights reserved. 32

6. 13 Intermolecular Forces Why is CH 4 a gas, H 2 O a liquid, and C 6 H 12 O 6 (glucose) a solid? Different intermolecular forces London dispersion forces Dipole-dipole forces Hydrogen bonds Copyright © Houghton Mifflin Company. All rights reserved. 33

6. 13 Intermolecular Forces Dipole-dipole forces Occur between polar molecules Molecules align so dipoles of opposite charge interact 5 - 25 k. J/mol (covalent bond 100 - 1000 k. J/mol) Copyright © Houghton Mifflin Company. All rights reserved. 34

Figure 6. 18 Dipole-dipole interactions between randomly arranged Cl. F molecules. Copyright © Houghton Mifflin Company. All rights reserved. 35

6. 13 Intermolecular Forces Hydrogen bonds A special case of dipole-dipole forces Occurs in compounds with N H, O H, or F H bonds N, O, H are very electronegative H is very small Molecules are very close 10 - 50 k. J/mol Copyright © Houghton Mifflin Company. All rights reserved. 36

Figure 6. 19 Depiction of hydrogen bonding among water molecules. The dotted lines are the hydrogen bonds. Copyright © Houghton Mifflin Company. All rights reserved. 37

Figure 6. 20 Diagrams of hydrogen bonding between selected simple molecules. Solid lines represent covalent bonds; dotted lines represent hydrogen bonds. Copyright © Houghton Mifflin Company. All rights reserved. 38

Figure 6. 21 If there were no hydrogen bonding between water molecules, the boiling point of water would be approximately -80 C. Copyright © Houghton Mifflin Company. All rights reserved. 39

6. 13 Intermolecular Forces London dispersion forces Temporary or induced dipoles Are found in all molecules Increase with "polarizability" Large atoms and/or molecules pi bonds (double or triple bonds) 1 - 50 k. J/mol Copyright © Houghton Mifflin Company. All rights reserved. 40

Figure 6. 22 Nonpolar molecules such as H 2 can develop instantaneous dipoles and induced dipoles. The attractions between such dipoles, through they are transitory, create London forces. Copyright © Houghton Mifflin Company. All rights reserved. 41

6. 13 Intermolecular Forces Intermolecular forces are heirarchical and additive All molecules have London dispersion forces; they are the only intermolecular forces in nonpolar molecules All polar molecules have dipole-dipole forces Hydrogen bonds are special Copyright © Houghton Mifflin Company. All rights reserved. 42

6. 13 Intermolecular Forces Gases: Intermolecular forces between molecules are not large enough to overcome kinetic energy (thermal energy) of individual molecules Molecules that are gases at room temperature usually have only London dispersion forces and/or are very small Copyright © Houghton Mifflin Company. All rights reserved. 43

6. 13 Intermolecular Forces Liquids: Intermolecular forces between molecules are about large enough to overcome most of thermal energy of the molecules Molecules that are liquids at room temperature usually have some combination of intermolecular forces, or are of moderate size Copyright © Houghton Mifflin Company. All rights reserved. 44

6. 13 Intermolecular Forces Solids: Intermolecular forces between molecules are large enough to overcome almost all of thermal energy of the molecules Molecules that are solids at room temperature have some combination of intermolecular forces, or are large Copyright © Houghton Mifflin Company. All rights reserved. 45

6. 13 Intermolecular Forces Phase changes and intermolecular forces: A substance melts at a temperature where thermal energy of the molecules is large enough to overcome some intermolecular forces A substance boils at a temperature where thermal energy of molecules is large enough to overcome most intermolecular forces. Copyright © Houghton Mifflin Company. All rights reserved. 46