Chapter 10: States of Matter Chemistry by Addison/Wesley

10.1 The Nature of Gases Kinetic Theory A gas is composed of particles Particles are small, hard spheres Particles in a gas move in a constant random motion Travel in straight paths and move independently of each other All collisions are perfectly elastic Kinetic energy is transferred without loss; total kinetic energy remains constant

Gas Pressure Gas pressure is the force exerted by a gas per unit surface area No particles = no pressure This empty space is called a vacuum Atmospheric pressure results from the collisions of air molecules with objects Barometers are devices used to measure atmospheric pressure Pascal (Pa) - SI unit of pressure

Pressure Atmospheric pressure at sea level is about 101.3 kilopascals (kPa) At sea level, the atmospheric pressure is strong enough to support a mercury column 760mm high One standard atmosphere is required to support 760 mm of mercury 101.3 kPa = 1 atm = 760 mm Hg

Energy and Temperature Objects tend to have a wide range of kinetic energy Most particles fall into an average range of kinetic energy Increase in average kinetic energy causes an increase in temperature Kelvin temperature is a relationship between the increase in temperature and average kinetic energy

10.2 The Nature of Liquids Unlike gases, the molecules of a liquid have attractive forces The molecules can move over one another which gives them the ability to flow Molecules vibrate and spin Adds to the molecules kinetic energy Still not enough kinetic energy to over come the attractive forces

Evaporation Vaporization is the conversion of a liquid to a gas or vapor When this occurs at the surface of a liquid that is not boiling, it is known as evaporation Those molecules with higher average kinetic energy are the ones that escape into a gas

Evaporation Evaporation of a liquid in a closed container causes an increase in vapor pressure Eventually, the number of particles condensing will equal the number of particles evaporating Increase in temperature will result in an increase in kinetic energy

Boiling Point The boiling point of a liquid is the point at which the vapor pressure equals the external pressure Boiling, like evaporation, is a cooling process The temperature never rises above the boiling point until all particles have been converted into a gas

10.3 Nature of Solids Molecules of a solid tend to vibrate around a fixed point Solids tend to dense an incompressible Melting point is the point at which the solid becomes a liquid Melting point is the same as the freezing point At this temperature, the solid and liquid substance are at equilibrium

Crystal Structure In a crystal, the atoms of the solid are arranged in a repeating pattern called a crystal lattice The shape of the crystal reflects the arrangement of the particles The type of bonding determines the melting point of the solid Crystals are arranged into seven crystal systems

Crystals The smallest unit of a crystal that retains the geometric shape is a unit cell Some solids can exist in more than one form Carbon is an example Diamond, graphite, and buckminsterfullerene These are known as allotropes

Amorphous Solids Amorphous solids lack internal order Glass is an example of an amorphous solid Glass is also called a super cooled liquid

10.4 Changes of State Phase Diagram is a representation of how temperature and pressure affect the state of matter In a phase diagram, the melting points and boiling points are plot on a graph as the temperature and pressure change The triple point is the point at which the two plot lines come together

Sublimation Sublimation is the conversion of a solid directly to a gas Freeze drying process uses sublimation Solid air fresheners and dry ice are also examples of materials the sublimate