States of Matter – Kinetic Theory

Chemistry Joke Once you’ve seen 6.02 x 1023 atoms… You’ve seen a mole!

Kinetic Theory Kinetic Theory explains the states of matter based on the concept that the particles in all forms of matter are in constant motion.

Kinetic Theory Gases—particles are far apart with no attraction or repulsion Liquids—particles can slide past one another but do experience attraction Solids—particles are not free to move but tend to vibrate about fixed points

Kinetic Energy and Temperature Directly Related Increase Temperature: Molecules move faster. Intermolecular forces can’t hold them together. Decrease Temperature: Molecules move slower. Intermolecular forces can now hold them together. Absolute zero (0 K) is the temperature at which the motion of particles theoretically ceases.

The Nature of Gases 3 basic assumptions of the kinetic theory as it applies to gases: #1. Gas particles are small, hard spheres with no volume (compared to the volume of the container) and experience no attraction or repulsion.

The Nature of Gases #2. Particles in a gas move rapidly in constant random motion but always in straight paths, changing direction only when colliding with one another or other objects.

The Nature of Gases #3. Collisions are perfectly elastic. This means no kinetic energy is lost when particles collide.

The Nature of Liquids Unlike gas particles, liquid particles are attracted to each other, but they are still able to slide past one another.

The Nature of Liquids The conversion of a liquid to a gas is called vaporization. When this occurs at the surface of a liquid that is not boiling, the process is called evaporation. Volatile liquids evaporate at room temp. A liquid will evaporate faster when heated—more kinetic energy to overcome intermolecular forces. But…evaporation is a cooling process because particles with the highest energy escape 1st!

The Nature of Liquids The boiling point (bp) is the temperature at which the vapor pressure of the liquid is equal to the external pressure on the liquid. Bubbles form throughout the liquid, rise to the surface, and escape into the air.

The Nature of Liquids Since the boiling point is where the vapor pressure equals external pressure, the bp changes if the external pressure changes. Normal boiling point is the bp at normal atmospheric pressure or 1atm.

The Nature of Solids Most solids have particles packed against one another in a highly organized pattern. Tend to be dense and incompressible

The Nature of Solids When a solid is heated, the particles vibrate more rapidly as the kinetic energy increases. At some point, the disruptive vibrations are strong enough to overcome the strong interactions. The melting point (mp) is the temperature a solid turns to liquid. The freezing point (fp) is the same temperature as the mp, but indicates the liquid becoming a solid.

The Nature of Solids Generally, most ionic solids have high melting points, due to the relatively strong forces holding them together. Molecular compounds have relatively low melting points.

Temperature Phase Diagram Pressure Critical Point Solid Liquid 1 Atm Triple Point Normal Boiling Point Gas Temperature

Pressure Temperature Phase diagram Solid Liquid 1 Atm Gas CONDENSATION FREEZING Pressure 1 Atm DEPOSITION Temperature

Pressure Temperature Phase Diagram Solid Liquid 1 Atm Gas MELTING VAPORIZATION Solid Air Fresheners! SUBLIMATION Temperature

Chemistry Joke A photon checks into a hotel and is asked if he needs any help with his baggage. No thanks, he says… I’m travelling light!