CHEM HAS A MANGINA
Terms in this set (77)
if a substance is at the same pressure and temperature what does the substance depend on to change
the kinetic energy of the particles and the strength of attraction between the two particles
which are stronger intramolecular forces or intermolecular forces
intra >> inter (between molecules)
What do Van der was forces refer to ?
the higher the polarity the *** the boiling point
what are LDF's
London dispersion forces, or dispersion forces, are attractions between an instantaneous dipole and an induced dipole.
*present in all molecules- polar or non polar
what affects strength of dispersion forces
shape of the molecule
what type of molecule would have stronger forces
long skinny ones > short fat ones (because surface area)
with increased molecular weight does the strength of dispersion forces increase or decrease
increase because Larger atoms have larger electron clouds which are easier to polarize.
If two molecules are of comparable size and shape, what force will be dominant?
dipole-dipole interactions is likely the dominating force.
If one molecule is much larger than another, what force will be
dispersion forces will likely determine its physical properties.
what bonds with hydrogen to form hydrogen bonding
what is viscosity
It is related to the ease with which molecules can move past each other.
what causes viscosity to increase
Viscosity increases with stronger intermolecular forces and decreases with higher temperature
how do gases liquify ?
by increasing pressure
what is a critical temperature?
the minimum temperature for liquefaction of a gas using pressure
what is critical pressure?
pressure required for liquefaction.
what is heat of fusion
is the energy required to change a solid at its melting point to a liquid.
when does a temperature not rise
The temperature of the substance does not rise during a phase change.
This is the pressure exerted by a substance in the gas phase
what happens when a liquid temperature increases
its vapor pressure increases
when does liquid boil
when the external pressure equals the vapor pressure
temperature of a boiling point increases as
how to get a liquid to bowl
increase temperature or decrease pressure.
equation predicts that a graph of In p versus 1/T should give a straight line with a slope equal to DHovap /R.
what do ion crystals try to do
ions pack themselves to maximize attractions and minimize repulsions
what does it mean if an ionic salt is soluble in water
If an ionic salt is soluble in water, it is because the ion-dipole interactions are strong enough to overcome the lattice energy of the salt crystal.
what are the three steps of forming a solution
-separation of solute particles (∆H1),
- separation of solvent particles (∆H2),
- new interactions between solute and solvent (∆H3).
delta H or energy change in a solution
can either be positive or negative
how to determine if delta H is positive or negative
To determine whether ∆Hsoln is positive or negative, we consider the strengths of all solute-solute, solvent-solvent, and solute-solvent interactions
breaking attractive intermolecular forces is always
H1 and H2 are always
H3 is always
Forming attractive intermolecular forces is always
increasing disorder leads to
lowers the energy of a system
If crystallization and dissolution are in equilibrium with undissolved solute,
is the amount of solute required to form a saturated solution
A solution with a concentration of dissolved solute that is less than the solubility
the solvent holds more solute
than is normally possible at that temperature
what causes greater solubility
The stronger the attraction between solute and solvent molecules
like dissolves like
The more similar the intermolecular attractions, the more likely one substance is to be soluble in another
larger molecules have
stronger dispersion forces
what doesn't change solubility
of liquids and solids does not change appreciably with pressure
what is the solubility of gas proportional to
Henry's law of gas and pressure
Sg = kPg
what happens because of solute- solvent intermolecular attraction
higher concentrations of nonvolatile solutes make it harder for solvent to escape to the vapor phase
what is an ideal solution
is one that obeys Raoult's law
Real solutions show approximately ideal behavior when
the solute concentration is low.
• the solute and solvent have similarly sized molecules.
• the solute and solvent have similar types of intermolecular attractions.
when does Raoult's law breakdown
when the solvent-solvent and solute-solute intermolecular forces are much greater or weaker than solute-solvent intermolecular forces.
Nonvolatile solute-solvent interactions also cause what to solution
have higher boiling points and lower freezing points than the pure
The change in boiling point is proportional
to the molality of the solution
what does delta T not depend on
what the solute is, but only on how many particles are dissolved
what type of solutions show greater changes
Since these properties depend on the number of particles dissolved, solutions of electrolytes (which dissociate in solution) should show greater changes than those of nonelectrolytes.
is a measure of the extent to which the electrolytes dissociates.
spontaneous reactions and changes
Processes that are spontaneous at one temperature may be nonspontaneous at other temperatures
when is it spontaneous for ice to melt
Above 0 C
when is the reverse process of ice to melt spontaneous
Below 0 C
what are spontaneous processes
how to predict spontaneity
both the enthalpy and entropy must be known
at a process occurring at one temperature what is the change in entropy equal to
the heat that would be transferred if the process were reversible divided by the temperature
when does entropy increase
- The number of independently moving molecules.
-when a solid is dissolved in a solvent
-Gases are formed from liquids and solids;
- Liquids or solutions are formed from solids;
- The number of gas molecules increases;
- The number of moles increases.
third law of thermodynamics
states that the entropy of a perfect crystalline substance is zero at absolute zero
at constant pressure what is delta h equal to
If G = 0
then the reaction is at equilibrium and no net reaction will occur.
G > 0
then the forward reaction is not spontaneous. However, the reverse reaction is spontaneous.
work must be supplied from the surroundings to drive the reaction.
what are analogous to standard enthalpies
of formation are standard free energies of formation
At equilibrium, Q = K, and G = 0
what happens when a system is approaching equilibrium
both the forward and reverse reactions are occurring
the forward and reverse reactions are proceeding at the same rate
law of mass action
Kc Is the equilibrium constant
The equation is referred to as equilibrium-constant expression which depends only on the stoichiometry of the reaction, not the mechanism
If K> 1
the reaction is product-favored; product predominates at equilibrium.
he reaction is reactant-favored; reactant predominates at equilibrium.
If The equilibrium constant of a reaction that has been multiplied by a number
is the equilibrium constant raised to a power that is equal to that number.
what does not appear in the equilibrium expression
solids and liquids
what does Q give you
gives the same ratio the equilibrium expression gives, but for a system that is not at equilibrium
To calculate Q
one substitutes the initial concentrations on reactants and products into the equilibrium expression.