Chapter 13 Section 1 Gases

Gas model Kinetic energy- energy due to motion Kinetic theory- tiny particles in all forms of matter are in constant motion. Gases are composed of particles that are small, hard, spheres. Gas particles are in rapid and constant random motion

Movement Gas particles travel in straight paths that are independent of each other. Gas particles will only change direction after a collision with another object. Collisions between gas molecules are elastic- no energy is lost.

Gas Pressure Gas pressure- the force exerted by a gas per unit of surface area of an object. It is the result of billions of simultaneous collisions of rapidly moving particles. Vacuum- empty space with no particles and no pressure. Atmospheric pressure- results from collisions of air molecules with objects.

Atmospheric pressure Barometers- measure atmospheric pressure. The SI unit of pressure is the pascal (Pa) One atmosphere(atm) is the pressure required to support 760mm of mercury in a barometer at sea level at 25 C So units could be pascals, kilopascals, atmospheres, mm of Hg, or torr. 1 atm = 760 mmHg= 760 torr =101.3 kPa

Kinetic energy and temperature When temperature rises, particles will move faster so they will have a greater kinetic energy. Kelvin temperature is directly proportional to average kinetic energy of particles.

Chapter 13 Section 2 Liquids

Kinetic theory Unlike gases, the particles in a liquid are attracted to each other. Vaporization- changing from a liquid to a gas. Evaporation- when vaporization occurs at the surface of a liquid that is not boiling. Vapor pressure- A force due to pressure of a gas above a liquid.

At constant vapor pressure, the number of vapor particles condensing equals the number of liquid particles vaporizing. This is called a state of equilibrium. Evaporation and condensation are still occuring, but there is no net change. Increase in temperature increases vapor pressure. Vapor pressure is measured with a manometer.

Boiling point The temperature at which vapor pressure of the liquid is equal to the external pressure. Boiling results when liquid is heated to a high enough temperature for the particles to turn into vapor. Normal boiling point- the boiling point of a liquid at a pressure of 101.3 kPa.

Chapter 13 Section 3 Solids

Solids The particles of solids are packed tightly together in an organized pattern. The melting point is the temperature that a solid turns into a liquid. A crystal is a substance in which the particles are arranged in a 3-dimensional orderly pattern. Ionic solids have high melting points, molecular solids have low melting points.

Unit cell- the smallest group of particles within a crystal that retain the geometric shape. Allotropes- two or more molecular forms of the same element in the same state. Amorphous solid- randomly arranged Glass- transparent solid that is the result of material cooling without crystalizing. Glasses do not melt but gradually soften when heated.

Chapter 13 Section 4 State Changes

Changes of state Boiling- liquid to gas Melting- solid to liquid Freezing – liquid to solid Condensation- gas to liquid Sublimation- solid to gas Desublimation- gas to solid

Phase diagrams Phase diagrams give the conditions of temperature and pressure at which a substance exists as solid, liquid, and gas. Conditions of equilibrium between two states are indicated by a line on the diagram. Triple point- The point where all three curves meet. All three phases exist at equilibrium with each other.