The Nature of Matter

Liquids The ability of gases and liquids to flow allows then to conform to the shape of their containers. Liquids are much more dense then gases.

More on liquids…. »Increasing the pressure on a liquid has hardly any effect on its volume. (The same is true of solids). »For that reason, liquids and solids are known as condensed states of matter.

Evaporation & Vaporization The conversion of a liquid to a gas or vapor is called vaporization. When such a conversion occurs at the surface of a liquid that is not boiling, the process is called evaporation.

Key Concept During evaporation, only those surface molecules with a certain minimum kinetic energy can escape from the surface of the liquid.

More on Evaporation…. Liquid evaporates faster when heated. This is because heating a liquid increases the average kinetic energy of its particles. As evaporation occurs, the particles with the highest kinetic energy escape first. Evaporation is a cooling process!!

Vapor Pressure Vapor (Gas) Liquid evaporation Condensation

An increase in temperature of a contained liquid increases the vapor pressure.

Boiling Point vapor pressure = external pressure When a liquid is heated to a temperature at which particles throughout the liquid have enough kinetic energy to vaporize, the liquid begins to boil. Because atmospheric pressure is lower at higher altitudes, boiling points decrease at higher altitudes.

Although vapor has the same kinetic energy as the liquid, its potential (or stored energy) is much higher. »Thus a burn from steam is more severe than one from an equal mass of boiling water at the same temperature.

The Nature of Solids The general properties of solids reflect the orderly arrangement of their particles and the fixed locations of their particles.

Melting Point LiquidSolid Melting Freezing

Crystal Structure The type of bonding that exists between particles in crystals determines their melting points. »Not all solids melt however. »Wood and cane sugar for example, decompose when heated.

Changes of State Sublimation is the change of a substance to a vapor without passing through the liquid state.

Phase Diagrams A phase diagram gives the conditions of temperature and pressure at which a substance exists as a solid, liquid and gas (vapor).

Phase Diagram Cont… The Triple Point describes the only set of conditions at which all three phases can exist in equilibrium with one another. A decrease in pressure lowers the boiling point and raises the melting point An increase in pressure will raise the boiling point and lower the melting point.