Kinetic Theory and a Model for Gases 13.1 Kinetic Theory and a Model for Gases Kinetic Theory and a Model for Gases The word kinetic refers to motion. The energy an object has because of its motion is called kinetic energy. According to the kinetic theory, all matter consists of tiny particles that are in constant motion.

Kinetic Theory and a Model for Gases 13.1 Kinetic Theory and a Model for Gases According to kinetic theory: The particles in a gas are considered to be small, hard spheres with an insignificant volume. The motion of the particles in a gas is rapid, constant, and random. All collisions between particles in a gas are perfectly elastic.

Kinetic Theory and a Model for Gases 13.1 Kinetic Theory and a Model for Gases Particles in a gas are in rapid, constant motion. Gases share some general characteristics. a) The rapid, constant motion of particles in a gas causes them to collide with one another and with the walls of their container. b) The particles travel in straight-line paths between collisions. c) A gas fills all the available space in its container.

Kinetic Theory and a Model for Gases 13.1 Kinetic Theory and a Model for Gases Gas particles travel in straight-line paths. Gases share some general characteristics. a) The rapid, constant motion of particles in a gas causes them to collide with one another and with the walls of their container. b) The particles travel in straight-line paths between collisions. c) A gas fills all the available space in its container.

Kinetic Theory and a Model for Gases 13.1 Kinetic Theory and a Model for Gases The gas fills the container. Gases share some general characteristics. a) The rapid, constant motion of particles in a gas causes them to collide with one another and with the walls of their container. b) The particles travel in straight-line paths between collisions. c) A gas fills all the available space in its container.

Gas Pressure How does kinetic theory explain gas pressure? 13.1

An empty space with no particles and no pressure is called a vacuum. 13.1 Gas Pressure Gas pressure results from the force exerted by a gas per unit surface area of an object. An empty space with no particles and no pressure is called a vacuum. Atmospheric pressure results from the collisions of atoms and molecules in air with objects.

13.1 Gas Pressure Gas pressure is the result of simultaneous collisions of billions of rapidly moving particles in a gas with an object.

A barometer is a device that is used to measure atmospheric pressure. 13.1 Gas Pressure A barometer is a device that is used to measure atmospheric pressure. At sea level, air exerts enough pressure to support a 760-mm column of mercury. On top of Mount Everest, at 9000 m, the air exerts only enough pressure to support a 253-mm column of mercury. Calculating What is the decrease in pressure from sea level to the top of Mount Everest?

The SI unit of pressure is the pascal (Pa). 13.1 Gas Pressure The SI unit of pressure is the pascal (Pa). One standard atmosphere (atm) is the pressure required to support 760 mm of mercury in a mercury barometer at 25°C.

Kinetic Energy and Temperature 13.1 Kinetic Energy and Temperature Kinetic Energy and Temperature What is the relationship between the temperature in kelvins and the average kinetic energy of particles?

Kinetic Energy and Temperature 13.1 Kinetic Energy and Temperature Average Kinetic Energy The particles in any collection of atoms or molecules at a given temperature have a wide range of kinetic energies. Most of the particles have kinetic energies somewhere in the middle of this range.

Kinetic Energy and Temperature 13.1 Kinetic Energy and Temperature The red and blue curves show the kinetic energy distributions of a typical collection of molecules at two different temperatures. INTERPRETING GRAPHS a. Inferring Which point on each curve represents the average kinetic energy? b. Analyzing Data Compare the shapes of the curves for cold water and hot water. c. Predicting What would happen to the shape of the curve if the water temperature were even higher? Even lower?

Kinetic Energy and Temperature 13.1 Kinetic Energy and Temperature Absolute zero (0 K, or –273.15°C) is the temperature at which the motion of particles theoretically ceases. Particles would have no kinetic energy at absolute zero. Absolute zero has never been produced in the laboratory.

Kinetic Energy and Temperature 13.1 Kinetic Energy and Temperature Average Kinetic Energy and Kelvin Temperature The Kelvin temperature of a substance is directly proportional to the average kinetic energy of the particles of the substance. In this vacuum chamber, scientists cooled sodium vapor to nearly absolute zero. To keep the atoms from sticking to the walls of the chamber, the scientists used magnetism and gravity to trap the atoms 0.5 cm above the coil in the center of the chamber. The coil is shown at about two times its actual size.

13.2 A Model for Liquids A Model for Liquids What factors determine the physical properties of a liquid?

13.2 A Model for Liquids Substances that can flow are referred to as fluids. Both liquids and gases are fluids. Both liquids and gases can flow. The liquid on the left is colored water. The gas on the right is bromine vapor. If a gas is denser than air, it can be poured from one container into another. These pictures were taken in a fume hood because bromine is both toxic and corrosive. Predicting Over time, what will happen to the gas in the uncovered beaker? Explain.

13.2 A Model for Liquids The interplay between the disruptive motions of particles in a liquid and the attractions among the particles determines the physical properties of liquids.

13.2 Evaporation Evaporation What is the relationship between evaporation and kinetic energy?

The conversion of a liquid to a gas or vapor is called vaporization. 13.2 Evaporation The conversion of a liquid to a gas or vapor is called vaporization. When such a conversion occurs at the surface of a liquid that is not boiling, the process is called evaporation.

13.2 Evaporation In an open container, molecules that evaporate can escape from the container. The process of evaporation has a different outcome in an open system, such as a lake, than in a closed system, such as a terrarium. a) In an open container, molecules that evaporate can escape from the container. b) In a closed container, the molecules cannot escape. They collect as a vapor above the liquid. Some molecules condense back into a liquid.

13.2 Evaporation In a closed container, the molecules cannot escape. They collect as a vapor above the liquid. Some molecules condense back into a liquid. The process of evaporation has a different outcome in an open system, such as a lake, than in a closed system, such as a terrarium. a) In an open container, molecules that evaporate can escape from the container. b) In a closed container, the molecules cannot escape. They collect as a vapor above the liquid. Some molecules condense back into a liquid.

13.2 Evaporation During evaporation, only those molecules with a certain minimum kinetic energy can escape from the surface of the liquid.

13.2 Vapor Pressure Vapor Pressure When can a dynamic equilibrium exist between a liquid and its vapor?

13.2 Vapor Pressure Vapor pressure is a measure of the force exerted by a gas above a liquid.

13.2 Vapor Pressure In a system at constant vapor pressure, a dynamic equilibrium exists between the vapor and the liquid. The system is in equilibrium because the rate of evaporation of liquid equals the rate of condensation of vapor.

Vapor Pressure and Temperature Change 13.2 Vapor Pressure Vapor Pressure and Temperature Change An increase in the temperature of a contained liquid increases the vapor pressure. The particles in the warmed liquid have increased kinetic energy. As a result, more of the particles will have the minimum kinetic energy necessary to escape the surface of the liquid.

13.2 Vapor Pressure

Vapor Pressure Measurements 13.2 Vapor Pressure Vapor Pressure Measurements The vapor pressure of a liquid can be determined with a device called a manometer.

Boiling Point Under what conditions does boiling occur? 13.2 Boiling Point Boiling Point Under what conditions does boiling occur? When a liquid is heated to a temperature at which particles throughout the liquid have enough kinetic energy to vaporize, the liquid begins to boil. The temperature at which the vapor pressure of the liquid is just equal to the external pressure on the liquid is the boiling point (bp).

Boiling Point and Pressure Changes 13.2 Boiling Point Boiling Point and Pressure Changes Because a liquid boils when its vapor pressure is equal to the external pressure, liquids don’t always boil at the same temperature. At a lower external pressure, the boiling point decreases. At a higher external pressure, the boiling point increases.

Altitude and Boiling Point 13.2 Boiling Point Altitude and Boiling Point A liquid boils when the vapor pressure of particles within the liquid equals the atmospheric pressure. The boiling point varies with altitude.

13.2 Boiling Point On the graph, the intersection of a curve with the 101.3-kPa line indicates the boiling point of that substance at standard pressure. INTERPRETING GRAPHS a. Analyzing Data What is the boiling point of chloroform at 101.3 kPa? b. Analyzing Data What is the vapor pressure of ethanol at 40°C? c. Analyzing Data What would atmospheric pressure need to be for ethanoic acid to boil at 80°C?

13.2 Boiling Point Normal Boiling Point Because a liquid can have various boiling points depending on pressure, the normal boiling point is defined as the boiling point of a liquid at a pressure of 101.3 kPa.

13.2 Boiling Point

The Nature of Solids 13.3 In 1985, scientists discovered a new form of carbon. They called this form of carbon buckminsterfullerene, or buckyball for short. You will learn how the arrangement of particles in solids determines some general properties of solids.

13.3 A Model for Solids A Model for Solids How are the structure and properties of solids related? The general properties of solids reflect the orderly arrangement of their particles and the fixed locations of their particles.

13.3 A Model for Solids The melting point (mp) is the temperature at which a solid changes into a liquid.

Crystal Structure and Unit Cells 13.3 Crystal Structure and Unit Cells Allotropes Allotropes are two or more different molecular forms of the same element in the same physical state. Allotropes have different properties because their structures are different. Only a few elements have allotropes.

Crystal Structure and Unit Cells 13.3 Crystal Structure and Unit Cells Carbon Allotropes Diamond, graphite, and fullerenes are allotropes of carbon. Classifying Based on the arrangements of their atoms, explain why the properties of fullerenes are closer to those of diamond than of graphite?

Crystal Structure and Unit Cells 13.3 Crystal Structure and Unit Cells Non-Crystalline Solids An amorphous solid lacks an ordered internal structure. Rubber, plastic, asphalt, and glass are amorphous solids. A glass is a transparent fusion product of inorganic substances that have cooled to a rigid state without crystallizing.

13.4 Sublimation Sublimation The change of a substance from a solid to a vapor without passing through the liquid state is called sublimation. Sublimation occurs in solids with vapor pressures that exceed atmospheric pressure at or near room temperature.

13.4 Sublimation When solid iodine is heated, the crystals sublime, going directly from the solid to the gaseous state. When the vapor cools, it goes directly from the gaseous to the solid state. When solid iodine is heated, the crystals sublime, going directly from the solid to the gaseous state. When the vapor cools, it goes directly from the gaseous to the solid state.

13.4 Phase Diagrams Phase Diagrams How are the conditions at which phases are in equilibrium represented on a phase diagram? A phase diagram is a graph that gives the conditions of temperature and pressure at which a substance exists as solid, liquid, and gas (vapor).

13.4 Phase Diagrams The conditions of pressure and temperature at which two phases exist in equilibrium are indicated on a phase diagram by a line separating the phases.

13.4 Phase Diagrams The conditions of pressure and temperature at which two phases exist in equilibrium are indicated on a phase diagram by a line separating the phases.

13.4 Phase Diagrams The triple point describes the only set of conditions at which all three phases can exist in equilibrium with one another. At the triple point, ice, liquid water, and water vapor can exist at equilibrium. Freezing, melting, boiling, and condensation can all occur at the same time, as shown in the flask.