Chapter 13 States of Matter

The KINETIC THEORY states that the tiny particles in all forms of matter are constantly in motion.

Assumptions of Kinetic Theory A gas is composed of particles. These particles are assumed to be small, hard spheres with insignificant volume relatively far apart from each other, between them is empty space. The particles in a gas move rapidly in constant random motion in straight paths. Change in direction is a result of a collision with its container or another gas particle. Aimless path of a gas particle is called a random walk. All collisions are perfectly elastic. In other words, no energy is lost in the collision.

All Matter As temperature decreases average kinetic energy decreases. ABSOLUTE ZERO is the temperature at which the motion of the particles in matter would theoretically stop. Absolute Zero is 0 K or -273oC

States of Matter

Gases Indefinite shape and indefinite volume Contains freely moving particles Gases

Gases Gas pressure is the force exerted by a gas per unit surface area of an object. A VACUUM is an empty space with no particles and therefore no pressure. Atmospheric pressure results from the collisions of air molecules with objects. Earth’s gravity keeps the particles close to Earth.

Gases Pressure is measured in PASCALS (Pa) usually by a barometer. Atmospheric pressure is 101.3 kPa. Other units include mm Hg and atmospheres (atm). 1 atm = 760 mm Hg = 101.3 kPa

Liquids Indefinite Shape and Definite Volume Particles can flow, but cannot move freely Liquids

Liquids Liquids, like gases, have the ability to slide past each other, known as the ability to flow. However, unlike gases, the particles in a liquid are attracted to one another.

Liquids Vaporization is the conversion of a liquid to a gas or vapor. Evaporation occurs when this conversion occurs at the surface of the liquid.

Liquids - Evaporation Molecules must have enough kinetic energy to overcome the attractive forces in the liquid to break away into a gas. Evaporation is a cooling process. Particles with the most kinetic energy leave the liquid first, lowering the average kinetic energy of the liquid.

Liquids - Evaporation In a closed container, some particles escape into the air above, but with nowhere to go, they collide with the walls of the container and produce a vapor pressure Vapor Pressure - force that results from the gas above a liquid. The particles go back and forth between the liquid and gas phases.

Liquids - Boiling When a liquid is heated, the kinetic energy of the particles increases throughout the liquid. The Boiling Point is the temperature at which the vapor pressure of the liquid is just equal to the external pressure. Vapor Pressure = External Pressure

Liquids - Boiling

Liquids - Boiling When the external pressure changes, the boiling point will also change. The normal boiling point is the boiling point of a liquid when the pressure is 101.3 kPa.

Liquids - Boiling Boiling like Evaporation is a cooling process. The particles with the highest kinetic energy are released as vapor, thereby lowering the average kinetic energy of the liquid. This is why water’s temperature doesn’t continue to increase when you boil it. It stays at 100oC

Solids Definite Shape and Definite Volume Particles vibrate about fixed positions Solids

Solids The particles in a solid, unlike liquids and gases, are not free to move about. They generally vibrate about a fixed point.

Solids As a solid is heated, the particles vibrate more rapidly and eventually have enough kinetic energy to overcome the attraction between the particles of the solid. The temperature when this happens is the melting point.

Solids Like liquids, the particles form an equilibrium with melting and freezing. In general, ionic solids have higher melting points because the forces between them are stronger.

Solids Most solids are crystalline. Crystals have repeating geometric patterns. Amorphous solids are solids with no crystalline form. Some believe that they are not in fact solids, but extremely thick liquids. Rubber, plastic, asphalt, and glasses are examples of amorphous solids.

Solids Crystalline vs. Amorphous When crystalline solids break, the broken angles are the same as the original substance. When amorphous solids break, the broken angles are jagged and irregular.

Phase Changes Solid → Liquid Melting Liquid → Solid Freezing Liquid → Gas Vaporizing Gas → Liquid Condensing Solid → Gas Subliming (Sublimation) Gas → Solid Depositing (Deposition)

Gas Liquid Solid Phase Change Latent Heat of Sublimation Latent Heat of Vaporization Latent Heat of Fusion

Phase Change Graph Temperature Energy

General Phase Diagram

Difference in Phase Diagram as a result of density

Phase Diagram for Water

Phase Diagram for Water