Gen Chem 2 / Module 2

mixture

contains more than 1 substance

solution

a homogenous mixture that exists as one phase

colloid

a heterogeneous mixture that exists as 2 or more phases

can be visibly distinct

solute

less abundant component(s) of a solution

solvent

most abundant component of a solution

miscible

soluble in any proportion

form 1 phase

most substances in nature are

mixtures

entropy

one of the factors that determines solubility

an energy form related to the number of ways the energy of a system can. be dispersed throught the motion of particles

the universe favors entropy

doesnt support order / requires work to order or to maintain order

entropy can also detemine solubility of a solute

both deltaH and deltaS are important

3 states of matter and entropy

S_gas > S_liquid> S_solid

solution usually has higher what?

entropy than solute and solvent

solution equilibrium

when solid is dissolving at the same rate of recrystalization

how can solutions be classified as?

based on quantity of solute dissolves relative to the maximum amount of solute

saturated solution

max quantity at a given temperature ( at equilibrium)

this quantity is the solubility of the solute

unsaturated solution

less than maximum ( add more solute it dissolves)

supersaturated solution

more than a saturated solution

an unstable situation

how is temperature affects solubility?

increased temp → increased motion ( KE ) → affects forces present

solids solubility

more stable as a higher temps

hheat encourages molecules to break free from lattice

gases solubility

less soluble with temperature increase

encourages molecules to overcome IFs and escape solution as a gas

Gas solubility ROT

1. gases are less soluble with increasing temperature because heat encourages molecules to overcome IFs and escape solution as a gas

2. gases are more soluble with increasing pressures because increasing pressure pushes molecules downward into the solution

Henry’s law

quantative relationship between gas pressure and solubility

S_gas is directly proportional to the partial pressure of the gas P above solution

Henry’s law equation

S_gas = kH x P_gas

molarity

amount of solute in mol / volume of solution in L

molality

amount of solute in mol / mass of solvent in kg

parts by mass

mass of solute / mass of solution

parts by volume

volume of solute / volume of solution

mole fraction

amount of solute in mol / amount of solute in mol + amount of solvent in mol

parts per million

(mass of solute / total mass of solution) x 106

colligative properties

depend only on the number of solute particles in solution and not on other properties of the solute

the presence of solute in a solvent alters the physical properties of the solvent

changes in colligative properties include

osmotic pressure

vapor pressure reduction

boiling point elevation

freezing point depression

underlying themes of colligative properties

• properties arise bc of solute particles can’t move between two phases

• presense of solute decreases the mol fraction of the solvent, which lowers the number of solvent particles leaving the solution per unit time

• the lowering requires a new balance in #’s of particles moving between 2 phases per unit time which results in the measured colligative property

• all properties can be used to calculate the molecular weight of a compound where osmotic pressure is the most reliable because it involves largest changes

Van’t Hoff factor

if a solute is a strong electrolyte then dissociation occurs where solute formula designates the number of particles

iTheoretical varies from iExperimental because of the non-ideal behaviour of solution

osmosis

the process by which solvent flows through a semipermeable membrane from a dilute to a concentrated solution

semipermeable membrane

allows water but not solute molecules to pass through it

osmotic pressure

the applied pressure required to prevent the net movement of water from the solvent to the solution

pressure is required to block osmosis

in osmosis, what 2 solutions are needed?

1 higher in concenration solution ( more dissolved solute) and 1 more dilute ( less dissolved solute)

reverse osmosis

a purification process in which solvent is forced through semipermeable membranes, leaving dissolved solutes behind

osmotic pressure equation

π = iMRT

Raoult’s law

when a non-volatile solute is dissolved in a liquid, the vapour pressure of that liquid is reduces

deltaP = i (X_solute x P_solvent)

Boiling point elevation

a solution boils at a higher temperature that pure solvent

since vp of a solution is lower than that of the pure solvent, need to go higher T before sufficient solvent vaporizes before it boils

deltaT_b = iK_bm

Freezing point depression

a solution freezes at a lower temperature

vp of solution lower than pure solvent, need to go to lower T before freeqing occurs

deltaT_f = iK_fm

chemical kinetics

the study of reaction rates

reaction rate

a measure of the changes in the concentration of reactants or products per unit time

what does each characteristic rate depend on

1. chemical nature of the reactants

2. a specific set of reaction conditions

rate

delta [ distance ] / delta t

rate of reaction

delta [ concentration] / delta t

rates can be monitores by following

reactants and products, reactant concentration occurs as product concentration increases

rate of reaction

-delta [ reactant ] / delta t

4 factors that can be controlled during a reaction that can affect reaction rate

1. concentration - molecules must collide to react

   • the higehr the concentration of reactants, the greater the reaction rate

2. physical state - molecules must mix to collide

   • different states have different ability to mix

3. temperature - molecules must collide with enough energy to react

   • the higher the temp the greater the reaction rate

   • at high temps, particles have more energy and therefore collide often and effectively

4. the use of catalysts - a chem agent that speeds up a reaction

   • lower the activation energy of a reaction

   • not used up in a reaction

rate law expression

aA + bB = cC + dD

rate law; k[A]^x [B]^x

1st order

rate directly proportional to concentration

• rate depends on [A]¹ and the reaction is first order with respect to A

• change in [A] causes the same exact change in rate

2nd order

rate is proportional to the square of concentration

• rate depends on [A]² and the reaction is second order respect to [A]

• change in [A] causes the square of that change in rate

0 order

reagent concentration has no effect on rate

• rate doesnt depend on [A], the reaction is 0 order with respect to [A]

• changes in [A] never affect rate

rate constant

k

proportionally constant that relates reaction rate to reactant and product concentrations