Chapter 13 States of Matter 13.1 The Nature of Gases 13.2 The Nature of Liquids 13.3 The Nature of Solids 13.4 Changes of State Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Objectives: Explain the kinetic theory in terms of gases. Perform pressure conversions using kPa, atm, and mmHg. Explain what pressure is and how it is measured. Describe how changes in temperature and pressure affect gases. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

What factors most strongly affect the weather? CHEMISTRY & YOU What factors most strongly affect the weather? The atmosphere is a gas, and the factors that determine the behavior of gases—temperature and pressure—affect the weather in the atmosphere. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

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. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Kinetic Theory and a Model for Gases According to the kinetic theory, all matter consists of tiny particles that are in constant motion. The particles in a gas are usually molecules or atoms. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Kinetic Theory and a Model for Gases The kinetic theory includes the following fundamental assumptions about gases. 1. The particles in a gas are considered to be small, hard spheres with an insignificant volume. Within a gas, the particles are relatively far apart compared with particles in a liquid or solid. Between the particles, there is empty space. No attractive or repulsive forces exist between the particles. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Kinetic Theory and a Model for Gases 2. The motion of particles in a gas is rapid, constant, and random. Bromine molecule Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Kinetic Theory and a Model for Gases Gases fill their containers regardless of the shape and volume of the containers. An uncontained gas can spread out into space without limit. The rapid, constant motion of particles in a gas causes them to collide with one another and with the walls of their container. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Kinetic Theory and a Model for Gases The particles travel in straight- line paths until they collide with another particle. The particles change direction only when they rebound from collisions. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Kinetic Theory and a Model for Gases 3. All collisions between particles in a gas are perfectly elastic. During an elastic collision, kinetic energy is transferred without loss from one particle to another. The total kinetic energy remains constant. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Describe an elastic collision between gas molecules. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Describe an elastic collision between gas molecules. An elastic collision is one in which kinetic energy is transferred from one particle to another with no overall loss of kinetic energy. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

How does kinetic theory explain gas pressure? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Gas Pressure Gas pressure is the result of billions of rapidly moving particles in a gas simultaneously colliding with an object. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Gas Pressure Gas pressure is the result of billions of rapidly moving particles in a gas simultaneously colliding with an object. If no particles are present, no collisions can occur. Consequently, there is no pressure. An empty space with no particles and no pressure is called a vacuum. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Gas Pressure Air exerts pressure on Earth because gravity holds the particles in air within Earth’s atmosphere. The collisions of atoms and molecules in air with objects results in atmospheric pressure. Atmospheric pressure decreases as you climb a mountain because the density of Earth’s atmosphere decreases as the elevation increases. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

A barometer is a device that is used to measure atmospheric pressure. Gas Pressure A barometer is a device that is used to measure atmospheric pressure. Vacuum Atmospheric pressure 760 mm Hg (barometric pressure) 253 mm Hg Sea level On top of Mount Everest 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. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

CHEMISTRY & YOU When weather forecasters state that a low-pressure system is moving into your region, it usually means that a storm is coming. What do you think happens to the column of mercury in a barometer as a storm approaches? Why? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

CHEMISTRY & YOU When weather forecasters state that a low-pressure system is moving into your region, it usually means that a storm is coming. What do you think happens to the column of mercury in a barometer as a storm approaches? Why? When a storm approaches, the column of mercury goes down, indicating a decrease in atmospheric pressure. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

The SI unit of pressure is the pascal (Pa). Gas Pressure The SI unit of pressure is the pascal (Pa). Normal atmospheric pressure is about 100,000 Pa, that is, 100 kilopascals (kPa). Two older units of pressure are commonly used. millimeters of mercury (mm Hg = torr) atmospheres (atm) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Gas Pressure One standard atmosphere (atm) is the pressure required to support 760 mm of mercury in a mercury barometer at 25°C. The numerical relationship among the three units is 1 atm = 760 mm Hg = 101.3 kPa. Recall that standard temperature and pressure (STP) are defined as a temperature of 0°C and a pressure of 101.3 kPa, or 1 atm. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Converting Between Units of Pressure Sample Problem 13.1 Converting Between Units of Pressure A pressure gauge records a pressure of 450 kPa. Convert this measurement to a. atmospheres b. millimeters of mercury Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Calculate Solve for the unknowns. Sample Problem 13.1 Calculate Solve for the unknowns. 2 Multiply the given pressure by the conversion factor. b. 450 kPa × = 3400 mm Hg = 3.4 × 103 mm Hg 101.3 kPa 760 mm Hg 1 atm a. 450 kPa × = 4.4 atm Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

What is the pressure in millimeters of mercury inside a vacuum? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

What is the pressure in millimeters of mercury inside a vacuum? 0 mm Hg Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Kinetic Energy and Temperature Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Kinetic Energy and Temperature As a substance is heated, its particles absorb energy, some of which is stored within the particles. This stored portion of the energy (potential energy) does not raise the temperature of the substance. The remaining absorbed energy speeds up the particles, which increases their kinetic energy. Increase in kinetic energy = increase in temperature. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Kinetic Energy and Temperature Average Kinetic Energy The particles in any gaseous substance at a given temperature have different kinetic energies. Most have kinetic energies somewhere in the middle of this range. Average kinetic energy describes the kinetic energy of a collection of particles in a substance. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Kinetic Energy and Temperature Average Kinetic Energy At any given temperature, the particles of all substances, regardless of physical state, have the same average kinetic energy. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Interpret Graphs The figure below shows the distribution of kinetic energies of water molecules at two different temperatures. The green curve shows the distribution of kinetic energy in cold water. The purple curve shows the distribution of kinetic energy in hot water. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Interpret Graphs The figure below shows the distribution of kinetic energies of water molecules at two different temperatures. Most of the molecules have intermediate kinetic energies, close to the average value. Notice that the molecules at the higher temperature have a wider range of kinetic energies. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Kinetic Energy and Temperature Average Kinetic Energy The average kinetic energy of the particles in a substance is directly related to the substance’s temperature. average kinetic energy of the particles = temperature of the substance. and vice-versa Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Kinetic Energy and Temperature Average Kinetic Energy Absolute zero (0 K, or –273.15oC) is the temperature at which the motion of particles theoretically ceases. No temperature can be lower than absolute zero. Absolute zero has never been produced in the laboratory. A near-zero temperature of about 0.000 000 000 1 K, which is 0.1 nanokelvin, has been achieved. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Kinetic Energy and Temperature Average Kinetic Energy The coldest temperatures recorded outside the laboratory are from space. Astronomers used a radio telescope to measure the temperature of the boomerang nebula. At about 1 K, it is the coldest known region of space. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

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. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

What is the result of increasing the temperature of a gas sample? A. A decrease in the average kinetic energy of the sample B. No effect on the sample C. An increase in the average kinetic energy of the sample D. The particles slow down. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

What is the result of increasing the temperature of a gas sample? A. A decrease in the average kinetic energy of the sample B. No effect on the sample C. An increase in the average kinetic energy of the sample D. The particles slow down. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

END OF 13.1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.