Download Physical Behavior of Matter Review

Physical Behavior of Matter Review
Matter is classified as a substance or a
mixture of substances.
The three phases of matter, i.e., solids, liquids,
and gases, have different properties.
• Drawing and
interpreting particle
diagrams are favorite
activities here.
A substance (element or compound) has a
constant composition and constant
properties throughout a given sample,
and from sample to sample.
• Distinguishing mixtures from pure substances
is a common question.
Elements are substances that are composed of
atoms that have the same atomic number.
Elements cannot be broken down by chemical
change.
A mixture is not a substance because it
is made up of two or more different
elements and/or compounds.
The proportions of components in a
mixture can be varied.
Each component in a mixture retains
its original properties.
Differences in physical properties such
as mass, particles size, molecular
polarity, boiling point, and solubility
permit physical separation of the
components of the mixture.
• Sometimes they ask about separating mixtures.
• Separations exploit differences in physical
properties: solubility (filtration or
chromatography), boiling point (distillation)
Energy can exist in different forms,
e.g., chemical, light, heat, nuclear.
• Energy conversion questions are common:
• chemical potential energy to kinetic energy
(exothermic rxns);
• chemical potential energy to electrical (voltaic
cells);
• electrical to chemical potential energy
(electrolytic cells)
• Nuclear energy to kinetic energy (fission and
fusion)
Heat is a transfer of energy (usually thermal
energy) from a body of higher temperature to a
body of lower temperature.
Thermal energy is the energy associated with
the random motion of atoms and molecules.
• Thermal energy = kinetic energy.
Temperature is the measure of the
average kinetic energy of the particles
in a sample of material.
Temperature is not a form of energy.
• The bolded sentence above is tested
somewhere on every single exam!!
Kinetic molecular theory (KMT) for an
ideal gas states:
• All particles are in random, constant, straight-line
motion.
• Gas molecules are separated by great distances
relative to their size; the volume of the gas
molecules is considered negligible.
• The molecules have no attractive forces between
them.
• Collisions between gas molecules may result in
the transfer of energy between gas particles, but
the total energy of the system remains constant.
• A consequence of statement b) is that equal
volumes of different gases at the same
temperature and pressure have the same
number of molecules.
Real and Ideal Gases
• Real gases have significant attractive forces
between them and/or are not separated by
great distances relative to their size.
• High pressures and low temperatures will
create these conditions for gases.
• Under conditions of life on earth, H2O behaves
as a real gas, while N2 and O2 behave ideally.
KMT Questions
Particles are in constant motion except
at absolute zero (zero Kelvin).
Kinetic molecular theory describes the
relationships of pressure, volume,
temperature, velocity, and frequency
and force of collisions.
Ideal Gas Equation
• You need to be able to use the ideal gas equation
(Table T). Any variable that is a constant can be
dropped from the equation.
• Free response questions usually only require setting up
the equation, not solving for it.
• Remember, Kelvin temperature must be used for all
gas law calculations!!!
• The formula for Celsius – Kelvin conversion is also on
Table T.
Ideal Gas Law Questions
The concepts of kinetic and potential
energy can be used to explain physical
properties that include:
fusion (melting),
solidification (freezing),
vaporization (boiling, evaporation),
condensation,
sublimation,
and deposition.
Sublimation questions are common,
deposition is rare.
Heating and Cooling Curves
• Most questions are
variations on heating
and cooling curves.
The horizontal lines
are the phase changes.
• Be sure you know
which one (meltingfreezing or boilingcondensing) is which
on the diagram.
At the melting point, solid and liquid
phases are in equilibrium with each other.
At the normal boiling point, liquid and gas
phases are in equilibrium.
A physical change results in the rearrangement
of existing particles in a substance.
A chemical change results in the formation of
different particles with changed properties.
Particle diagrams are commonly used on the
regents to demonstrate phase changes.
Chemical and physical changes can be
exothermic or endothermic.
• Table I shows heats of reaction (ΔH) for a
number of combustion reactions, a bunch of
synthesis reactions (often called the heat of
formation), and some solubility changes (a
physical change).
• There is usually one question using this table
on every test.
• Often they ask for which reaction is
endo/exothermic. Three have to have the
opposite sign to the correct answer.
Which Reference Table Do I Use?
Phase Changes of Water
• Physical changes of water are given special
attention.
• Information can be found on Table B. You
should know when and how to use the “heat”
equations on Table T.
• For phase changes, q=mHf and mHv. For liquid
water temperature increases and decreases,
q=mcΔT is used.
The structure and arrangement of particles
and their interactions determine the
physical state of a substance at a given
temperature and pressure.
Intermolecular Forces
• Intermolecular forces created by the unequal
distribution of electrons result in varying
degrees of attraction between molecules.
• Hydrogen bonding is an example of a strong
intermolecular force.
• Small molecules that have equal or symmetrical
charge distributions are non-polar, and are gases
to very low temperatures and pressures (that is,
they behave ideally under most conditions).
• Larger molecules, even those with symmetrical
charge distributions, have larger attractive forces
and higher boiling points and melting points.
• The boiling point (distillation) is used to
separate crude oil (a mixture of hydrocarbons)
into fractions based on molecular size.
• Unequal distribution of charge is a
euphemism for a polar molecule. These
molecules have dipoles [partial (+) and (–)
parts of the molecule].
• For similar molecules, the larger the dipole,
the higher the melting point and boiling point
are.
Hydrogen Bonding
• Hydrogen “bonding” is the strongest dipole
force. Only N, O, and F form hydrogen bonds.
• Although it may seem obvious, hydrogen
bonds are only between these elements and
hydrogen: N – H , O – H, and H – F.
• Remember, hydrogen bonding is not a true
“bond”; it has 5% of the strength of a covalent
bond.