Section 1

Kinetic Theory: How particles in matter behave 3 Basic Assumptions of the Kinetic Theory 1.All matter is composed of small particles (atoms, molecules, and ions) 2.The particles are in constant, random motion 3.The particles are colliding with each other and the walls of their container

Look at Figure 2 – Does the ice cube appear to be moving? Atoms in a solid are held tightly in place by the attraction between the particles. The attraction between the particles is what gives solids a definite shape and volume

Thermal Energy: Total energy of a materials particles Includes kinetic = vibrations and movement within and between the particles Also Potential = Forces that act within or between particles What does the thermal energy do to the particles in the solid cube? Causes them to vibrate What happens if we lower the temperature of a substance? Vibrate slower

Molecules have kinetic energy at all temperatures – even absolute zero Which molecules move slower – molecules at 0 degrees C or 100 degrees C? Molecules at 0 degrees Temperature therefore relates to the average kinetic energy of particles in the substance or how fast the particles move

Particles in a solid are closely packed together Have a geometric arrangement of particles Chemical and physical properties of a solid are attributed to the type of geometric arrangement Example: Ice Cube

What happens to a solid when thermal energy or heat is added to it? As the thermal energy is added the particles on the surface of the ice cube vibrate faster The particles on the surface transfer energy to other particles Eventually the particles have enough kinetic energy to overcome the attractive forces

Melting point: Temperature at which a solid begins to liquefy When the particles have enough kinetic energy to slip out of the ordered arrangement the ice melts Energy IS required for the particles to slip out of the ordered arrangement Heat of Fusion: Amount of energy required to change a substance from the solid phase to the liquid phase at its melting point

Do particles have more kinetic energy as a solid or liquid? Liquid What does the extra kinetic energy allow the particles to do? Partially overcome the attractions to other particles Allows particles to slide past each other Allows liquids to flow Allows liquids to take the shape of their container The attraction between particles is not quite overcome which is why liquids have a definite volume

Do gas particles have enough kinetic energy to overcome the attraction between them? Yes Gases do not have a fixed volume Fill the container they are in

How does a liquid become a gas? The particles in a liquid are constantly moving Some have more kinetic energy than others Particles moving fast enough can escape the attractive forces When particles escape the attractive forces they can enter the gas state This process is called vaporization

2 ways vaporization can occur? 1.Evaporation 2.Boiling Evaporation Vaporization that occurs at the surface of a liquid Can occur at temperatures below the liquids boiling point Have to have enough kinetic energy to escape the attractive forces of the liquid

Boiling occurs at a specific temperature Depends on the pressure on the surface of the liquid Boiling Point: Temperature at which the pressure of the vapor in the liquid is equal to the external pressure acting on the surface of the liquid External pressure = force pushing down on a liquid to keep the particles from escaping Heat of vaporization: Energy required for the liquid at its boiling point to become a gas

Gas particles are moving quickly and are far apart Do not have a definite shape or volume Diffusion: Particles spread throughout the volume until they are evenly distributed Example: Spraying air freshener in one half of the room