Ch 12 Section 2 Flashcards
molecules or ions of the solute are
attracted by the solvent
because the dissolution process occurs at the surface of the solute, it can be speeded up if the surface area of the solute is
increased
in general, the more finely divided a substance is, the greater the surface area per unit mass and the more
quickly it dissolves
very close to the surface of a solute, the concentration of dissolved solute is
high
stirring or shaking helps to disperse the solute particles and bring fresh solvent into
contract with the solute surface
the effect of stirring results in increased contact between the
solvent and the solute surface
as the temperature of the solvent increases, solvent molecules move faster, and their
average kinetic energy increases
at higher temperatures, collisions between the solvent molecules and the solute are more frequent and are of higher energy than at
lower temperatures
this helps to separate solute molecules from one another and to disperse them among the
solvent molecules
for every combination of solvent with a solid solute at a given temperature, there is a limit to the amount of solute that can be
dissolved
the point at which this limit is reached for any solute solvent combination is difficult to predict precisely and dpends on the nature of the
solute, nature of the solvent, as well as the temperature
as more solid dissolves and the concentration of dissolved molecules increases, collisions become more
frequent
eventually, molecules are returning to crystal at the same rate at which they are going into solution, and a dynamic equilibriuim is established between
dissolution and crysstallization
solution equilibrium is the physical state in which the opposing processes of dissolution and crystallization of a solute occur at
equal rates
a solution that contains the maximum amount of dissolved solute is described as a
saturated solution
a solution that contains less solute than a saturated solution under the existing conditions is an
unsaturated solution
when a saturated solution of a solute whose solubility increases with temperature is cooled, the excess solute usually comes out of solution, leaving the solution satureated at the
lower tempearture
sometimes, if the solution is left to cool undistrubted, the excess solute does not separate and a
supersaturated solution is produced
a supersaturated solution is a solution that contains more dissolved solute than a saturated solution contains under the
same conditions
a supersaturated solution may remain unchanged for a long time it if is not disturbed, but once crystals begin to form, the process continues until equilibrium is
reestablished at the lower temperature
the solubility of a substance is the amount of that substance required to form a saturated solution with a specific amount of … at a specified …
solvent; temperature
the temperature must be specified because solubility varies with
temperature
for gases, pressure must also be
specified
the rate at which a solid dissolves is unrelated to its solubility at that
temperature
the maximum amount of a given solute that dissolves and reaches equilibrium is always the same under the
same conditions
“like dissolves like” is a useful rule for predicting whether one substance will
dissolve in another
what makes substances similar depends on the type of bonding, the polarity or nonpolarity of molecules, and the intermolecular forces between the
solute and solvent
the polarity of water molecules plays an important role in the formation of solutions of
ionic compounds in water
the slightly charged parts of water molecules attract the ions in the ionic compound and surround them to keep them separated from the other
ions in the solution
this solution process with water as the solvent is referred to as
hydration
as ydrated ions diffuse into the solution, other ions are exposed and are drawn away from the
crystal surface by the solvent
the entire crystal gradually dissolves and hydrated ions become unifromly
distributed in the solution
when crystallized from aqueous solutions, some ionic substances form crystals that incorporate water
molecules
these crystalline compounds, hydrates, retain specific ratios of water molecules and are represented by formulas such as
CuSO4 . 5H2o
heating the crystals of hydrate can drive off the wter of hydration and leave the
anhydrous salt
when a crystalline hydrate dissolves in water, the water of hydration returns to
the solvent
the behavior of a solution made from a hydrate is no different from the behavior of one made from the
anhydrous form
dissolving either form results in a system containing
hydrated ions and water
ionic compounds are generally not soluble in
nonpolar solvents
the nonpolar solvent molecules do not attract the ions of the crystal strongly enought to overcome the forces holding the
crystal together
liquids that are not soluble in each other are
immiscible
nonpolar substances are generally quite soluble in
nonpolar liquids
the only attractions between the nonpolar molecules are
london forces
the intermolecular forces existing in the solution are therefore very similar to those in
pure substances
liquids that dissolve freely in one another in any proportion are said to be
miscible
changes in pressure have very little effect on the solubilities of
liquids or solids in liquid solvents
increases in pressure increas gas
solubilities in liquid
when a gas is in contact with ther surface of a liquid, gas molecules can
enter the liquid
as the amountof dissolved gas increases some molecules begin to escape and reenter the
gas phase
an equilibrium is eventually established between the rates at which gas molecules enter and leave the
liquid phase
as long as this equilibrium is undistrubed, the solutibility of the gas in the liquid is unchanged at a given
pressure
gas + solvent ⇌
solution
increasing the pressure of the solute gas above the solution puts stress on the
equilibrium
molecules collide with the liquid surface more
often
the increase in pressure is partially offset by an increase in the rate of gas molecules entering the
solution
in turn the increase in the amount of dissolved gaas causes an increase in the rate at which molecules escape from the liquid surface and become
vapor
eventually equilibrium is restored at a
higher gas solubility
an increase in gas pressure casues the equilibirium to shift so that more molecules are in the
liquid phase
the solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid:
henry’s law
henry’s law applies to gas liquid solutions at
constant temperature
when a mixture of ideal gases is confined in a constant volume at a constant temperature, each gas exerts the same pressure it would exert if it occupied the space
alone
assuming that the gases do not react in any way, each gas dissolves to the extent it would dissolve if no other gases were
present
the rapid escape of a gas from a liquid in which it is dissolved is known as
effervescence
increasing temperature usually decreases
gas solubility
as the temperature increases, the average kinetic energy of the molecules in solution
increases
a greater number of solute molecules are able to escape from the attraction of solvent molecules and return to
the gas phase
at higher temperatures, equilibrium is reached with fewer gas molecules in solution, and gases are generally less
soluble
the effect of temperature on solubility of solids in liquids is more difficult to
predict
often, increasing temp increases solubility of
solids
however, an equibalent temp increase can result in a large increase in solubility for some solvents and onlyt a
slight change for others
in some cases, solubility of a solid decreases with an
increase in temperature
the formation of a solution is accompanied by an
energy change
the formation of a solid liquid solution can apparently either absorb energy or
release enrgy as heat
during the formation of a solution solvent and solute particles experience changes in the forces attracting them to other
particles
befor3e dissolving begins solvent molecules are held together by
intermolecular forces (solvent solvent attaction_
in the solute molecules are held together by
intermoelcular forces (solute solute attraction)(
energy is requoired to separate solute molecules and solvent moecules from their
neightbors
a solute particle that is surrounded by solvent molecules is said to be
solvated
the net amount of energy absorved as heat by the solution when a specific amount of solute dissolves in a solvent is the
enthalpy of solution
thyou know tghat heating decreases the solubility of a gas, so dissolution of gases is
exothermic
in the gaseous state, molecules are so far apart that there are virtually no intermolecular forces of
attraction between them
therefore the solute solute interaction has little effect on the
enthalpy of a solution of a gas
energy is relreased when a gas dissolves in a liquid because attraction between solute gas and solvent molecules outweighs the energy needed to separatge
solevent molecules
Enthalpy of solution is negative when energy is
Released
Enthalpy of solution is positive when energy is
Absorbed
Energy is absorbed when solute particles becoming
Separated from solid
Energy is absorbed when solvent particles being moved apart to allow
Solute particles to enter liquid
Energy being released when solvent particles being attracted to and
Solvating solute particles
