Download The nature of matter

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
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Fixed shape
Not compressible
Rigid
Dense
Liquid: medium interactions
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Liquid
Not rigid
Assumes shape of container
Not compressible
Dense
Gas: no interactions
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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
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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 = 101 000 kPa
 Pounds/square inch
 Atmospheric pressure = 14.7 lb/in2
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
22.414 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
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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)
1
P
V
Charles’ Law
 As temperature increases,
volume increases (P, n
constant)
 Temperature must be
measured in Kelvin
V T
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:
 P1V1/T1 = P2V2/T2
 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)
V n
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 = p1 + p2 + p3 + …
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 CO2 in the liquid is kept
in solution
 Open the cap and the CO2 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.