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