States of Matter

Kinetic Theory Tiny particles in all forms of matter are in constant motion A gas is composed of particles that are positioned far away from one another. Between particles is empty space and no forces attract or repel between the particles Particles move in constant random motion All collisions are perfectly elastic

Gas Pressure The force exerted by a gas per unit surface area of an object. Air exerts pressure on Earth because gravity hold air molecules in Earth’s atmosphere Vacuum = if there are no gas particles present, there cannot be any collisions, and there is no pressure

Measuring Pressure Barometers measure atmospheric pressure SI unit is pascal (Pa): sea level is 101.3 kPa mmHg: sea level is 760 mmHg Standard atmosphere: sea level is 1 atm 101.3kPa = 760mmHg = 1atm

Liquids Liquids are able to flow like gases. However, the particles in a liquid are attracted to each other by intermolecular forces Most particles do not have enough kinetic energy to escape into a gaseous state

Vaporization Conversion of liquid to a gas vapor Evaporation occurs at the surface when the object isn’t boiling Molecules must have a high enough kinetic energy to become a gas

Vapor Pressure Force of gas above a liquid When liquids are in a closed container and evaporated, the gas will eventually exert enough pressure that the rate of evaporation will equal the rate of condensation

Boiling Point The temperature at which the vapor pressure of the liquid is just equal to the external pressure

Solids Particles in solids vibrate around fixed points. They are packed together in highly organized patterns

Melting Point The temperature at which a solid turns into a liquid The vibrations are strong enough to overcome the interactions that hold them in fixed positions

Unit Cell Solids form crystalline shapes The smallest group of particles within a crystal that retains the geometric shape of the crystal is known as a unit cell

Allotropes Two or more different molecular forms of the same element in the same physical state

Diamond Graphite Buckyball

Amorphous Solids Solids that lack ordered internal structures Also called super cooled liquids Rubber, plastic, asphalt, glass

Phase Diagrams Gives the conditions of temperature and pressure at which a substance exists as solid, liquid, and gas Triple point is the point where all three phases can exist in equilibrium with one another

Sublimation The change of a substance from a solid to a vapor without passing through the liquid state Solids have vapor pressure Dry Ice