The States Of Matter All matter is made of something, even if it looks like nothing. We make classifications according to its properties, both chemical and physical

Three States of Matter Solid: strong interactions  Fixed shape  Not compressible  Rigid  Dense

Liquid: medium interactions  Liquid  Not rigid  Assumes shape of container  Not compressible  Dense

Gas: no interactions  Not rigid  Completely fills container  Compressible  Low density

Plasma: the fourth state  At very high energies (temperatures) all the electrons are removed from the atoms  Not an important state for chemistry

Atom motion and temperature  Atoms in molecules have three types of motion  Rotation – moving about the centre of mass  Vibration – vibrating about the centre of mass  Translation – movement of the centre of mass  As temperature increases, the energies of all types of motion increase

Solids  Atoms in solids rotate and vibrate but do not translate  Melting occurs when the translational energy of the atoms is sufficient to break free of the lattice  Usually this is a very well defined point  With amorphous solids it can be smeared out – softening of fats

Vapour pressure and boiling  Molecules do not all have the same energy  High energy molecules escape the liquid – vapour pressure  When vapour pressure = atmospheric pressure boiling occurs  Sublimation is direct transition of solid to gas (dry ice)

Kinetic molecular theory and pressure – a case for atoms  Pumping up a tire increases the number of molecules  Pressure is caused by the energetic molecules striking the tire wall  More molecules – higher pressure  Higher temperature – higher pressure

Under pressure  Gases exert pressure by virtue of motion  Gravity makes the air density higher near the earth’s surface  Pressure decreases with elevation

Atmospheric pressure  The weight of the air supports a column of mercury 760 mm high  Barometer is used for measuring atmospheric pressure  Atmospheric pressure changes with the weather

The atmosphere is layered  Troposphere  Where the weather happens  Stratosphere  Where the ozone is  Mesosphere  Ionosphere  The brutal strength of solar radiation ionizes all the components – permits transmission of radio signals around the earth without need of mirrors

Units of pressure  mm (or cm) of mercury  Atmospheric pressure = 760 mm Hg  Pascal is SI unit for pressure  Atmospheric pressure = kPa  Pounds/square inch  Atmospheric pressure = 14.7 lb/in 2

Standard temperature and pressure (STP)  Standard conditions allow direct comparison of properties of different substances  Standard temperature is 273 K (0ºC)  Standard pressure is 760 mm Hg  At STP, 1 mole of any ideal gas occupies L

Gas laws: experience in math form  The properties of gases can be described by a number of simple laws  The laws establish quantitative relationships between different variables  They are largely intuitively obvious and familiar

The four variables  Pressure (P)  Volume (V)  Temperature (T in Kelvin)  Number of molecules (n in moles)

Variables and constants  In the elementary gas laws two of the four variables are kept constant  Each law describes how one variable reacts to changes in another variable  All the simple laws can be integrated into one combined gas law

Boyle’s law  The first experimental gas law  Pressure increases, volume decreases (T, n constant)

Charles’ Law  As temperature increases, volume increases (P, n constant)  Temperature must be measured in Kelvin

Absolute zero  Gay-Lussac observed V changed by 1/273 of value at 0ºC  Plotted as V = kT (T = ºC + 273), V = 0 at T = 0  Does the gas actually occupy zero volume?  No, at lower T the law is not followed

Combined gas law  Fold together Boyle and Charles:  P 1 V 1 /T 1 = P 2 V 2 /T 2  Given five of the variables, find the sixth  Units must be consistent  Temperature in Kelvin

Gay-Lussac and law of combining volumes  When gases react at constant temperature and pressure, they combine in volumes that are related to each other as ratios of small whole numbers  His experiments with hydrogen and oxygen had implications for the understanding of the atom and the structures of simple molecules

Avogadro’s Law  As the number of moles of gas increases, so does the volume (P, T constant)

Dalton’s law of partial pressures  A mixture of gases exerts a pressure as if all the gases were independent of one another  Total pressure is the sum of the pressures exerted by each one  P = p 1 + p 2 + p 3 + …

Real world applications 1: Henry’s Law and sodie pop  The quantity of gas dissolved in a liquid depend directly on the pressure of that gas above the liquid  Under pressure the CO 2 in the liquid is kept in solution  Open the cap and the CO 2 rapidly escapes

Real world applications 2: The science of breathing  The gas laws explain the mechanics of breathing: the transport of oxygen from the lungs and exchange with carbon dioxide produced in the body.