Chem 302 Unit 1/2

Because ΔH and ΔS always have the same sign, ΔG of a phase change is always

temperature dependant

-ΔG means a reaction is spontaneous

for -ΔH and -ΔS: ΔG is negative at low temps (going down a phase)

for +ΔH and +ΔS: ΔG is negative at high temps (going up a phase)

calculating a phase transition temperature:

T_phase=ΔH/ΔS

If the reaction occurs spontaneously then ΔG:

is negative/below 0

if the reaction doesn’t occur spontaneously then ΔG:

is positive/above 0

when you are at equilibrium (equally between phases) ΔG:

is 0 (definition of equilibrium)

Higher IMF means _____ vapor pressure

lower

higher temp means _____ vapor pressure

exponentially higher

vapor pressure is a _____ phenomenon

surface

vapor pressure is _____ of volume

independant, bc pressure is collisions with container

vapor pressure is measured when gas and liquid phases…

are at equilibrium

unique thing about H₂O phase diagram:

negative slope for solid/liquid line, indicated solid is less dense than liquid because ice can melt at a lower temperature when pressure is highered (think of biting an ice cube and it melts)

because of the very strong hydrogen bonds/attraction in water molecules

ΔH_vap is:

always positive

ΔH_vap of water

40 kJ/mol

ΔH_vap of of HOCH₂CH₂OH (ethylene glycol)

60 kJ/mol

ΔH_vap of C₆H₁₄ (hexane)

30 kJ/mol

ΔH_vap of helium

2 kJ/mol

at triple points on phase diagram:

all three phases in equilibrium

at lines on phase diagram:

two phases in equilibrium

Substances with large heats of vaporization produce

low vapor pressures at room temperatures.

the Clausius Clapeyron applies when:

at equilibrium when ΔG=0

For the same substance at the same temperature, vapor pressure

will always be equal

HIGHER IMF MEANS _____ VAPOR PRESSURE

LOWER

Ideal gas constant

8.3 J/mol

Higher ΔH_vap:

stronger bonds/IMFS, lower vapor pressure

the phase with the smallest heat capacity will have:

the largest slope on a heat supplied vs temp graph and increase in temp most when the same amount of heat is added

if Q<K

reaction shifts right

if Q>K

reaction shifts left

free energy is temperature ______

dependant

as entropy decreases, free energy _____

increases

adding solute to a mixture always _____ the entropy

increases

When solute is added to the solvent, the entropy of the system _________ so the free energy _________ which means the boiling point _________ and the freezing point ______

increases

decreases

increases

decreases

calculating vapor pressure in a binary system

P_tot=P_A+P_B

P_A=P^o_AX_A

P_B=P^o_BX_B

Where P^o is pure vapor pressure

and X is the mole fraction of the compound

these can be found using common sense instead of calculation

ΔH_soln of NaCl

positive

ΔH_soln of CaO

negative

ΔH_soln =

ΔH_soln=ΔH_C.L.+ΔH_hyd

ΔH_C.L is always positive (energy needed to break bonds)

ΔH_{hydration/solvation} is always negative (amount of energy released after forming solute-solvent IMFs)

If increasing T increases solubility

reaction is endothermic, ΔH_soln is positive

if increasing T decreases solubility

reaction is exothermic, ΔH_soln is negative

ΔS is usually _____ for dissolving salts

positive

If a reaction is exothermic, it shifts right when T is

lower

If a reaction is endothermic it shifts right when T is

higher

If ΔH_rxn is negative (exothermic) then

increasing T shifts the reaction to the left as K2<K1

If ΔH_rxn is positive (endothermic) then

increasing T shifts the reaction to the right as K2>K1

the cation with the _______ will precipitate first

lowest molar solubility

the farther apart the K_sp values are in the same form…

the easier it is to selectively precipitate

7 Strong Acids

HBr HCl HI HNO₃ HSO₄ HCLO₃ HCLO₄

6 strong bases

LiOH NaOH KOH RbOH Sr(OH)₂ Ba(OH)₂

Arrhenius theory

acids and bases are the dissociation products for water

Add an H⁺ for acids

Add an OH^- for bases

Bronsted-Lewis Theory: Bronsted

built around the proton

bronsted acid is a proton donor, loses one H and gains a charge of -1, becomes a conjugate base after donating (HCOOH, HCL, NH4)

bronsted base is a proton acceptor, gains one H and gain a charge of +1, becomes a conjugate acid (HCOO, CL, NH3)

Bronsted Lewis Theory: Lewis

built around the same unbonded lewis pair from chem 301

lewis base has unpaired electrons (:NH₃)

lewis acid has empty orbits and binds to lewis base (borane, BH₃₎

THE SPECTATORS

salts of strong acids: Cl, Br, I, NO3, ClO4, ClO3

salts of strong bases Li, Na, K, Rb, Ba, Sr

the larger the K_a

the stronger the acid

the larger the K_b

the stronger the base

the stronger the acid the ____ the conjugate base

weaker

the weaker the base

the higher the pOH

the weaker the acid

the higher the pH

deriving the autoprotolysis of water from RICE

assume 55.4-x=55.4

application of rice for strong acids/bases

assumes all of a strong acid disassociates

assume water doesn’t dissascociate much

appliying RICE to weak acids/bases

assume water doesn’t disassociate much

assume C-x=Capplying RICE

applying RICE to buffers

assume water doesn’t disassociate much

assume C-x=Capplying RICE

at room temp K_w

10^-14

at room temp pK_w

14

pK_a and pK_b

same theory as pH/pOH

pay attention to the suffix- is it a or b? ensure correct conversion

completing a weak acid/base calculation

1. remove any spectators

2. identify as a weak acid or base using HA, BH+, A-, or B

3. solve using (KaCa)^1/2 or (KbCb)^1/2

4. convert to the correct answer format

Spectators

form an acid (anion, negative charge): Br Cl I NO₃ SO₄ CLO₃ CLO₄

form a base (cation, positive charge): Na Li K Rb Ba Sr

ln 1

0

ln 2

0.7

ln 3

1.1

clausius clapeyron equation

ln(^P1/_P2) = ^ΔH_vap/_R (1/T₁ - 1/T₂)

three types of gas interactions with with water

reaction: compound has a chemical reaction with water

like dissolves like: polar gasses dissolve readiily

inert, non-polar gasses: ΔS = (-) bc gas to liquid

ΔH = (-) because an IMF is forming

ΔG is negative at low temps

this is why there is more o2 dissolved in colder water

gasses in water are more/less soluble at higher temps

less

in inert gases dissolving in water, the _____ term causes the gas to become less soluble at higher temps

entropy

non-polar molecules are miscible with

other non-polar molecules

polar molecules are miscible with

other non polar molecules and salts (but not hydrocarbons)

polar molecules:

asymmetrical

permanent dipoles

h-bonding

-OH, -C-OH, -N-H

non-polar molecules

dispersion forces

symmetrical

hydrocarbons/lots of -CHx groups

—CH₂CH₂CH₃, SF₆, O₂

osmotic pressure change

π=iMRT

i=van’t hoff factor

M=molarity (mols solute/L solution)

T=temp in kelvin

freezing point depression/boiling point elevation

ΔT_f = 𝑖∙𝐾𝑓∙𝑚

ΔT_b = 𝑖∙𝐾𝑏∙𝑚

i-van’t hoff factor

k_f/b= freezing/boiling point constant

m=molality (moles solute/kg solvent)

using R in the osmotic pressure equation

Use 0.082 (pressure in ATM is being used)

since room temp is 300K, RT=25

solubility chart/understanding

species with a multiple charge are typically insoluble (except for sulfate)

nitrates, chlorates, and ammonium salts are always soluble

alkali metals (first column on periodic table) and halogens (second to last column on periodic table) are always soluble

molar solubility

how much salts dissociate and ionize in water

larger number=most soluble

smaller number=least soluble

to find molar solubility given the K_sp

K_sp divided by number of ions/root number of ions yk what I mean

common ion calculation

1. identify the common ion and the insoluble salt (IS). common ions show up in both compounds and the insoluble salt will have a given Ksp

2. write the Ksp expression for the insoluble salt

3. plug in the concentration of the common ion directly

4. solve for the concentration of the other ion (this is it’s new molar solubility)

systems move in the direction that

removes stress

reaction direction info

exothermic: heat on the right, adding heat shifts left

endothermic: heat on the left, adding heat shifts right

decreasing an aqueous compound shifts towards that compound

solids/liquids don’t affect equilibrium

pressure changes only affect gasses