Chp 13; The molecular nature of matter and change
Across a period in a periodic table
from group 1a to group 2a the 2a ion has a smaller radius and higher charge, so its chrge density and deltaH hydr are greater
foam
gas dispersed in a liquid
the particles in a solution generally have a
greater freedom of movement than the particles in a pure solute
A saturated solution
is at equilibrium and contains the maximum amount of dissolved solute at a given temperature in the presence of undissolved solute
entropy (S)
is directly related to the number of ways a system can distribute its energy, which involves the freedom of motion of the particles
solubility in hexane is high for
large alcohols
substances that have similar intermolecular forces are able to dissolve in each other
like dissolves like
aerosol
liquid or solid dispersed in a gas
solubility in hexane is
low for the smallest alcohol
a solution containing nonvolatil solute always boils at a higher temperature than the pure solvent. the vapor pressure of the solution is
lower than the vapor pressure of the pure solvent; hence the solution must be heated to a higher temperature in order for the vapor pressure to equal the external pressure.
emulsion
one liquid dispersed in another
there is a change in entropy (deltaS) associated with a phase change, it can be
positive or negative. when a liquid vaporizes is positive (deltaSvap= Sgas-Sliquid). the change in entropy when a liquid freezes (fusion)is negative (deltaSfus<0)
ion-dipole forces are the
principal force involved when an ionic compound dissolves in water
Colligative properties are
properties of a solution that depend only on the number of solute particles in a given volume of solution, not on their type
The freezing point depression of a solution is directly
proportional to the molality of the solute in solution. The molality of a solution is a concentration ratio that is calculalted as molality= moles of solute/ mass of solvent kg
the change in the vapor pressure is
proportional to the mole fraction of the solute in the solution
A solution containing a nonvolatile solute will have a lower vapor pressure than the
pure solvent (salt in boiling water). The change in the vapor pressure is proportional to the mole fraction of the solute in the solution
dilute and concentrated are
qualitative
solubility is a
quantitative term
a supersaturated solution is an unstable solution that temporarily contains more than the maximum solute possible at a particular temperature, due to
rapid cooling
gas solubility in water decreases with
rising temperature
Which step involved in the formation of a solution is associated with a positive sing for deltaH?
-Solute and solvent particles separate from each other
sol
solid dispersed in a liquid
N2(g) decrease volume
solubility increases
entropy usually increases when a solution forms because there are more interactions between particles in a
solution
a solute dissolves in a
solvent to form a solution.
miscible
the substances are soluble in each other at any quantity
freezing point depression is observed for solutions containing nonvolatile solute
the vapor pressure of a solution is lower than of the pure solvent and the solution therefore freezes at a lower temperature
The ration moles of solute/L of solution is called the molality of a solution (M), whereas the molarity (m) of the solution is expressed s moles of solute/ kg of solvent.
for an aqueous solution, these two quantities will be very similar if the solution concentration is low
Henry's law
expresses the quantitative relationship between gas pressure and solubility. The solubility of a gas (Sgas) is directly proportional to the partial pressure of the gas (Pgas) above the solution Sgas=kH x Pgas
deltaH hydr of the ion=
(always <0)
Alcohols are orgaic compounds that have a dual polarity, a polar hydroxyl (-OH) group bonded to a nonpolar hydrocarbon group:
- The -OH portion interacts through strong H bonds with water and through weak dipole-induced dipole forces with hexane. - The hydrocarbon portion interacts through dispersion forces with hexane and through very weak dipole-induced dipole forces with water
the charge of an ion to heat of hydration
- as the charge on an ion increases and its radius decreases, its charge density will increase and so will the magnitude of the heat of hydration -an ion with a higher charge has a more negative heat of hydration than an ion of similar size but lower charge
structures and behaviors of colloids
-a colloid in H2O is stabilized by ion-dipole forces between the charged surfaces of the colloid particles and the H2O molecules - colloids particles will coagulate and settle from the dispersion if the colloid is heated -there are different types of colloids by the physical state of their components
describe gas-liquid solutions
-a nonpolar gas will not dissolve readily in a polar solvent -a polar gas will dissolve readily in a polar solvent - gases appear to be more soluble in aqueous solution if they react with H20 after dissolving
nonvolatile, nonelectrolyte
-a solute that has a negligible vapor pressure at the boiling point of the solvent -a solute that dissolves but produces no ions in solution
describe the freezing point depression for a solution?
-deltaTf is a positive value. Since deltaTf=Kfm it will be a positive value. This value should be subtracted from the freezing point of the pure solvent. -freezing point depression is proportional to the molality of the solution -only the solvent freezes at the freezing point of the solution, leaving solute particles behind. The freezing point of the solution is lower because its vapor pressure is lower. - the freezing point constant Kf is characteristic of the solvent
the heat of solvation for a solution process
-if deltaHhydr <0, it indicates that the more energy is release due to solvent-solute attraction than the energy absorbed in separating solvent particles - the heat of solvation is the enthalpy charge that occurs when a solute particle is surrounded by solvent particles - the heat of solvation is called the heat of hydration if H20 is the solven
the osmotic pressure of a solution
-is the pressure that needs to be applied to prevent the next flow of solvent between solutons that are separated by a semipermeable membrane -is directly proportional to the molarity of the solution -is not affected by the total volume present -increases with temperature -flow from a less concentrated to a more concentrated solution
A solution that is in contact with undissolved solute at a given temperature
-the concentration of dissolved solute will not change - the solution is saturated because it contains the maximum amount of dissolved solute in a fixed quantity of a particular solvent at a given temperature - undissolved solute is in equilibrium with dissolved solute -the rate at which solute is dissolving is equal to the rate at which solute particles are crystallizing from solution
the van't Hoff factor i is a measure of the effect of a solute on colligative properties. It is given by the ratio measured value for electrolyte solution/expected nonelectrolyte solution.
For any electrolyte i>1 because an electrolyte dissociates in solution
The charge density of an ion has a significant effect on its heat of hydration.
The higher the charge on an ion and the smaller its size, the greater its attraction to the H2O molecules surrounding it and the more negative the value of delta H hyd of the ion
colloid is
a dispersion of particles in a dispersing medium; particles are too small to settle out, but large enough to scatter light
if a solution process is endothermic
a solution will still be able to form if delta S is large
a solution has higher entropy than the pure solute and pure solvent
because the number of ways to distribute the energy is related to the number of interactions between different molecules. There are far more interactions possible when solute and solvent are mixed than when are pure Ssoln>(Ssolute+Ssolvent) or deltaSsoln>0
pressure has little effect on the solubility of liquids and solids because they are almost incompressible
but it has a major effect on the solubility of gases
Coulomb's law says that the higher the charge of an ion and the smaller its radius, the
closer it gets to the oppositely charge pole of an H2O molecule and the stronger the attraction.
since deltaS for a solution process is usually positive and favorable, a large change in entropy will
compensate for the unfavorable enthalpy change
an unsaturated solution
contains less than the equilibrium concentration of dissolved solute
a supersaturated solution
contains more than the equilibrium concentration and is unstable relative to the saturated solution
deltaH solvation=
deltaH solvent + deltaH mix
deltaHsoln=
deltaHsolute + deltaHhydr
a nonpolar solute in a polar solvent
dipole-induced dipole forces
a nonpolar solute in a polar solvent that also contains dissolved ions
dipole-induced dipole forces
The attractive forces between I2(S) + H2O are
dipole-induced forces.
the solubility of a gas in water is
directly proportional to the pressure of the gas
present in all solutions principal intermolecular force when both solvent and solute are nonpolar
dispersion forces
An alcohol possesses a polar hydroxyl (-OH) group and a non polar hydrocarbon chain.
due to its dual polarity, an alcohol is able to dissolve in both polar and nonpolar solvents
the most favorable solution process involves an increase in entropy and a decrease in enthalpy
entropy usually increases when a solution forms. An increase in entropy accompanied by a decrease in enthalpy is extremely favorable
a solution is a homogeneous mixture meaning it exists in one phase, whereas a colloid is a
heterogeneous mixture with two or more phases in its composition
solubility in water is
high for smaller alcohols
solution
homogeneous mixture
solvation in water is called
hydration
when an ionic solute dissolves in water the ions separate and each ion becomes surrounded by a cluster of H2O molecules called a
hydration shell
both enthalpy and entropy changes determine whether or not a given solvent-solute pair will form a solution. A solution process for which deltaHsoln>0 will still be spontaneous if it is counter-balanced by a corresponding
increase in the entropy of the system
O2 (g) increase P
increase solubility
an ionic solute in a polar solvent
ion-dipole forces
colloid
is a type of heterogeneous mixture,
the solubility of solute is the
maximum amount that dissolves in a fixed quantity odf a given solvent at a given temperature, when an excess of the solute is present
the magnitude of the heat of hydration of an ion decreases down the group on the periodic table and increases from left to right across a period. (the term magnitude indicates the value of the heat of hydration, not its sing)
moving down a group on the periodic table, the charge on an ion remains the same but its size increases. Less heat is released during the hydration process for a larger ion. The magnitude of the heat of hydration therefore decreases down the group, but increases across a period
most solids are more soluble at higher temperatures
sulfate are some exceptions
solution formation involves the interplay of two factors
systems change toward a state of lower enthalpy and higher entropy, so the relative sizes of deltaHsol and deltaSsoln DETERMINE WHETHER A SOLUTION FORMS
down a group in the periodic table
the charge stays the same and the size increases; thus the charge density decreases, as do the deltaH hydr values
solvent
the component present in the largest amount
solute
the component present in the smallest amount
How does the presence of a strong electrolyte in solution affect the colligative properties of a solution when compared to the same number of moles of a nonelectrolyte solute?
the electrolyte dissociates or ionizes to give a large number of moles of dissolved particles, with greater effect on the colligative properties
heat of hydration exhibit trends based on the ion's charge density, the radio of its charge to its volume.
the higher the charge density, the more negative deltaHhydr is.
solubility
the maximum amount of a solute that can dissolve in a fixed quantity of a particular solvent at a given temperature
the more freedom of motion the particles have
the more ways they can distribute their kinetic energy, a liquid has higher entropy than a solid Sgas>Sliquid>Ssolid
in an ideal solution of a strong electrolyte, the van't Hoff factor i is equal to
the number of moles of particles produced by dissociation of 1 mol of the electrolyte
hydration shells
the number of water molecules in the innnermost shell depends on the ion's size; four fit tetrahedrally around small ions like Li+
in a solid
the particles are fixed in their positions with little freedom of motion
in gas
the particles have little restriction and much more freedom pf motion
ion-dipole forces are
the principal force involved when an ionic compound dissolves
in liquids
they can move aroud each other and so have greater freedom of motion
A solution forms when the attractive forces between the solute and solvent are similar in strength
to the solvent-solvent and solute-solute attractions and are therefore able to replace them
a solution usually has a higher entropy than either the pure solvent or pure solute because in the solution there are a greater number of interactions between particles and therefore more ways to distribute the energy of the system
true
like dissolves like rule
when the forces within the solute are similar to those within the solvent, the forces can replace each other and a solution forms
An increase in pressure will cause the solubility of a gas to increase
whereas the solubility of a liquid or solid will usually not change much