Review for 3rd Exam
Chapter 5
In Chapter 5 you were introduced to the variables which describe the "state" of an ideal gas.
Ideal gas law calculations are then used to determine: P,V, T, n, Mm(molar Mass) or the density.
You needed to be familiar with the different units associated with each of these variables.
Pressure is in terms of atm, torr, mmHg (P =
; temp in tems of K (must be able to convert to
K), volume in terms of cm3, mL, L etc. You should know the following conversions: 1000 cm3 =
1000 mL = 1L. To convert from mL to L, simply move the decimal point three places to the left.
(ie. 25.0 mL = 0.0250L). Many gases at room temperature and pressure can be considered to be
"ideal gases" as there are minimal effects of the forces between the molecules making up the gas.
There are essentially four types of ideal gas law calculations:
1. Calculate the values of P, V, n, and/ or T of a system, given the variables for the same system
at a different condition, and noting which variables are constant.
2. Calculate the value of one of the variables (P, V, n, or T) given the other three , or information
about the other three.
3. Calculate the value of the Molar Mass (Molecular Weight) of the gas given the density and P
and T, or calculate the density given the molar mass and P and T.
4. Calculate the pressure, volume or # of moles of gaseous reactant necessary to make a certain
amount of product, or the pressure, volume, or # of moles of a product given the amount of
reactant AND THE BALANCED CHEMICAL EQN for the STOICHIOMETRY!
Boyle's Law, Charles' Law, and the combined gas law can be obtained from PV = nRT (ideal gas
law) by holding the right variable constant. (REMEMBER the temperature must be in _____!
In addition to the ideal gas law you should know Dalton’s Law of Partial Pressure.
Remember this law applies when you collect a gas over water You must take into account the
vapor pressure of the water (Ptotal = Pproduct + Pwater). You should know the postulates on which
the Kinetic Theory of Gas is based. How is the speed of the gas related to the Temperature.
What about the kinetic energy. What is the relationship between the speed of the gas and the
molar mass? You should remember that the rate of effusion of a gas is proportional to 1/(Mm)½ .
You should be able to calculate the molar mass of a gas based on its relative rate of effusion
(Graham’s Law of effusion)
What is the difference between effusion and diffusion. What makes a gas an ideal gas?
Under what conditions does it become a real gas. What do the temperature and pressure have to
be for the gas to be non-ideal (high pressure, low temp.).WHY? What Eqn of state can be used
to describe real gases?
Chapter 12
In chapter 12, you should take note of the reemphasis that the molecules are much closer
together in the liquid and solid phases than in the gas phase. Since they are closer,
intermolecular (BETWEEN molecules) forces are going to be much more important. The
boiling point is defined as the temperature at which the vapor pressure of the liquid equals the
atmospheric pressure. The normal boiling point is the temperature at which a substance boils at 1
atm. If the intermolecular forces are weak, then the molecules are not held tightly together in the
liquid phase. Thus they would have a higher vapor pressure. What would be the trend in the
other properties like: viscosity, surface tension, melting pt., boiling pt.. You should know the
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types of intermolecular forces (physical forces) that exist. From weakest to strongest (for
molecules of similar mass) they are London Dispersion (induced-dipole induced dipole), dipole
forces, and Hydrogen Bonding, HFON forces. The London dispersion forces are a result of
temporary dipoles, or induced dipoles forming as a result of movement of the electron cloud.
Large, more massive, substances tend to have more mobile electrons so in non-polar molecules,
more massive molecules will have a higher boiling point (Stronger London). If the molecule is
polar and has a dipole moment, then it has a stronger intermolecular force due to a partial
electrostatic attraction. This is carried to an extreme in the hydrogen bonding since Fluorine,
Oxygen, and Nitrogen are the most electronegative elements and when combined with hydrogen,
they form an extremely polar bond. So hydrogen bonds are the strongest.
You should be familiar with the terms molecular solid, metallic solid, ionic solid, and
network covalent. Network covalent substances usually result from combinations of group 13,
14, 15, and sometimes 16 atoms with themselves (diamond) or combinations with one of the
other above mentioned groups, SiO2, Silicon Carbide, Boron nitride, etc. They are very high
melting since as in an ionic solid, there are actual chemical bonds between all of the species
making up the solid. You should know a few examples for each type. Remember that if a
substance is a liquid or a gas at room temp and pressure, then that substance is likely to be a
molecular substance. You should know the trends in boiling point and melting point for the
different types of solids. Also know information about their properties such as conductivity.
You should know the trends within the different types of solids, i.e. the lowest melting metals are
on the left side of the periodic table, and the higher the charges on the ions in an ionic solid, the
greater the melting temp.
What are the main crystalline unit cell types? What are simple cubic, body-centered
cubic, and face centered cubic unit cells. How many atoms does each type of cell contain.
Given the length of the unit cell side or the radius of the atoms making up the cell you should be
able to determine the cell volume and therefore the density. Or given the density you should be
able to determine the length of one side of the unit cell and/or the radius of the atoms in the cell.
Remember, the relationship used to determine this depends upon the cell type, How is the length
of the side of a cubic unit cell determined (X-ray)? For molecular solids such as solids formed
from Ar, Kr, or Xe how are the crystals packed?
You should be familiar with the concept of vapor pressure. The vapor pressure is a
function of the temperature as seen by the liquid vapor equilibrium line (ln(P) vs 1/T is linear).
Also be able to use the Claussius Clapeyron equation to calculate either the vapor pressure at
another temp, or the temp at which a particular vapor pressure is achieved given the boiling point
or other vapor pressure information, or the heat of vaporization for a particular liquid given
vapor pressure information. What is the heat of vaporization? You should be able to identify
and define the following areas on a phase diagram: solid region, liquid region, gas region, triple
point, critical point, vapor-liquid equilibrium line, vapor-solid equilibrium line, solid liquid
equilibrium line, constant pressure process, melting process, constant temperature process,
boiling process, sublimation process. Can you determine the vapor pressure of a liquid at a
particular temperature from this diagram? What are the axes labels?
Chapter 13
Chapter 13 restates and expands on several concepts that were covered in previous chapters
specifically regarding solutions. Solution, solute, solvent, solubility, concentration, mass %, and
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molarlty are all concepts that were introduced and treated in previous chapters. We now classify
the solutes according to whether they are electrolytes, (strong and weak), or nonelectrolytes.
These classifications depend on whether the substances form ions in solution, whether they are
soluble or insoluble in the solution, and/or whether they are strong or weak acids and bases. You
should be familiar with other concentration units: such as mole fraction, volume %, mole %, and
molality (m) in addition to molarity (M), and mass %. You should be able to perform dilution
calculations based on the idea that moles of solute before dilution moles of solute after. For
concentrations in molarity for example: M * Va = Mb * Vb.
You should also be able to switch between the following concentration units: mass%,
mole%, molarity, and molality. Remember the hints in the book on what to use as a basis. To
determine whether one substance will dissolve in another, we can use the rule of thumb that "like
dissolves like. Basically, this means that if a substance is polar it will dissolve in a polar solvent,
if it is nonpolar it will dissolve in a nonpolar solvent. Temperature affects the solubility of a gas
in a liquid, liquid in liquid, and solid in liquid. Generally as the temperature increases, the
solubility decreases for a gas in a liquid, BUT the solubility of a liquid or solid solute can
increase with increasing temp. (generally speaking) although in some cases the solubility
decreases. This can be explained by considering that heat is generally required when a solid or
liquid is dissolved (endothermic process), but is liberated when a gas is dissolved or in the case
of some ionic compounds (exothermic process). This depends on the relative sizes of the lattice
enthalpy and the energy of hydration. Increasing pressure causes a gas solute to become more
soluble, but has little effect on a liquid or solid solute. You should be familiar with Henry's Law
and how to use it. What is Raoult’s Law and an ideal solution?
You should realize that the properties of the solution are going to be different from the
properties of the pure solvent or the pure solute. The properties of a solution which are different
from the pure solvent are called colligative properties. The colligative properties depend on the
number of particles in solution, not on just the moles of solute. This means that for salts such as
NaCl there are two particles in the solution instead of one. This is taken into account in the Vant
Hoff’s factor “i”. You should be familiar with and be able to calculate vapor pressure lowering,
freezing point depression, boiling point elevation, and osmotic pressure. Osmosis can cause red
blood cells to shrink or bloat, if you get an injection which is not isotonic, at the same particle
concentration as your blood. Essentially, the solvent flows to the more concentrated side to
dilute it. Freezing point depression is routinely used to melt ice on sidewalks by adding salt, and
eggs or spaghetti will cook faster. If we add salt to the water since the boiling point is elevated.
Remember the Kf and Kb values are specific to the solvent.
How do detergents work? What is a micelle? Define saturated solution and supersaturated
solution.
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