DAT Gen Chem everything you need to know

avogadro’s number

1 mol of any element = 6.022 × 10 ^ 23

% composition

mass / mm comp * 100

empirical vs molecular formula

empirical = simple reduced formula

molecular = the regular formula

empirical to molec

given / empirical (standard) , then multiply that by the subscripts

% composition to empirical formula

1) turn % into grams, then divide those grams by its molec mass, then divide again but with the smallest molec mass

what is limiting reagent and how to find it

LR = the compound that cant fully covert the other reactant

1) balance eqn, 2) convert to mols, 3) pick one reactant to determine how much of the other reactant was used.

density of water

1 g/mL

how to find % yield

actual / theor * 100

actual = given

theor = calced using LR (the expectations)

% error

|Experimental - Actual | / Actual * 100

how to find mols

moles = mass (g) / mm (g/mol)

how to find Molarity (M)

M = mols solute / L soln

how to find molality (m)

m = mols solute / kg of solvent

solute vs solvent?

solute = cute = small = salt

solvent = vater = water

how to find Normality (N)

N = nM

n = equivalents

M = Molarity

how to find mol fraction of solute (Xsolute)

Xsolute = mols solute / tot mols in soln

BP elevation equation?

deltaT_b = k_bim

i = vant hoff factor (# of particles that the solute splits into)

m = molality

k_b = bp constant

FP Depression eqn?

deltaT_f = -k_fim

how to find osmotic pressure?

pi = iMRT

(remember: PERMIT)

pi = osmotic pressure

R = .082 L*atm/mol*K

Raoult’s Law?

P_A = X_AP°_A

P_A = VP soln

X_A = mol fraction of solvent

P°_A = pure VP of solvent

Ideal Gas Law

PV = nRT

n = # mols

R = .082 L*atm/mol*K OR 8.3 J/mol*K (usually .082)

P = pressure

Graham’s Law of Effusion

r2/r1 = √M1 / √M2

r = rate of effusion

M = mm (not molarity)

Dalton’s Partial Pressure

P_A = (X_A)(P_Total)

Xa = mol fraction of gas A

Combined Gas Law?

P₁V₁/ n₁T₁ = P₂V₂ / n₂T₂

V ∝ T (when everything else is constant)

Dalton’s Law

P_Total = P_A + P_B + ...

how many gas laws?

5

boyle’s gas Law (Gas Density)

P1V1 = P2V2

P ∝ 1/ V

Avogadro’s Law

V1 / n1 = V2 / n2

V ∝ n

(n = mols)

Gay-Lussac’s Law

P1 / T1 = P2 / T2

P ∝ T

Charle’s Law

V1 / T1 = V2 / T2

V ∝ T

Diatomic atoms

Have No Fear Of Ice Cold Beer

H2 , N2, F2, O2, I2, Cl2, Br2

how to find density of a gas?

Density (rho) = P (MM) / RT

MM = molar mass

how would you rank boiling points

based on the type of bond

Ionic bond (metal + nm) > H-Bond > DD > LDF (unbranched molec) > LDF (branched)

which force is stronger, intramolecular forces or intermolecular forces?

intramolecular forces are stronger , they are the ones that hold the actual bonds of the molec tg

whats the realtionship bw LDFs and molec size?

the larger the molec, the more LDFs it has

what type of molec has dipole-dipole?

polar molecs (diff ENs)

note: symmetric molecs have their dipoles cancel out = no net dipole

note: incr pressure = incrs DD

which forces do NP covalent bonds have?

ONLY LDFs

NP covalent = unequal sharing of e’s

which forces do Polar covalent bonds have?

DD + LDF

equation for internal energy? (ΔE)

ΔE = q + w

if W = (-) then system did work on surround (aka expansion )

if W = (+) then surround on system (aka compression)

equation for work?

w = -PΔV

if ΔV < 0 (decr) = w (+)

if ΔV > (incr) = w (-)

what does ΔH > 0 and ΔH < 0 mean?

ΔH > 0 = endothermic = absorbed heat (melt, vaporize, sublime)

ΔH < 0 = exothermic = released heat (freeze, condense, deposition)

3 ways that heat transfers?

conduction = thru direct contact

convection = thru motion (ex: hot air balloon)

radiation

what does it mean when work is + or - ?

if w = (-) then system did work on surround (aka expansion )

if w = (+) then surround on system (aka compression)

qsystem + q surround = ?

0

equation to find q (amt of heat absorbed/released)

q = mcΔT

m= mass

(to remember: mcat)

equation for bomb calorimetry

qcal = cΔT

qrxn = -qcal

equation for bond dissociation energy / bond energies/ enthalpies (breaking/forming bonds)

ΔH°rxn = ΣΔH° _{Bonds broken (reactants)} - ΣΔH° _{Bonds formed (products)}

_{bond energies will be given! (ex: C-H, Cl-Cl, etc.)}

_{breaking bond = endothermic}

_{forming bond = exothermic (more stable)}

enthalpy of formation

ΔH°rxn = ΣΔH°_{f (products)} - ΣΔH°_{f (reactants)}

_{heat of formation of molecules will be given!}

what is Hess’s Law

the sum of enthalpy changes

(u have to match up the rxns given to the og rxn by multiplying/adding and then cancel out any identical molecs that appear on both sides of the rxns)

what is the 2nd and 3rd law of thermodynamics?

2nd = entropy always incrsing

3rd = entropy of crystalline substances @ 0 K is 0. (bc no KE = no entropy)

eqn for entropy (S)

ΔS = ΣnS°(products) - ΣnS°(reactants)

in what 3 ways can you increase entropy (ΔS > 0)?

1) incrs dissolution (aq)

2) incr temp (higher temp = higher KE = higher disorder)

3) incr products of rxn

is low entropy or high entropy more favored?

high entropy (= low energy) (when ΔS > 0)

what phases can you go from for ΔS>0 ?

solid —> liq —> gas (more KE = more disorder)

Gibb’s Free Energy eqn

ΔG° = ΔH° - T ΔS°

when is rxn spont, nonspont, and at eq?

ΔG < 0 = spont (exergonic = strong bonds formeD)

ΔG > 0 = nonspont (endergonic = weak bonds formed)

ΔG = 0 = @ eq

General Rate Law Equation

aA + bB → cC + dD

Rate = k[A]^m[B]ⁿ

rate law units for 0 order and 1st order?

Zero Order: Ms-1

First Order: s-1

rate law units for 2nd order and 3rd order?

Second order: M-1s-1

Third Order M-2s-1

Arrhenius Equation

k=Ae^-Ea/RT

^{e = 2.718}

^{A = pre-exponential factor}

^{Ea inversely proportional to k (rate constant)}

different bw intermediates and catalysts?

intermediates act as a product then a reactant

catalysts act as reactant then a product (remember: CARP)

what 2 factors increase the rate constant k (which incrs the rxn rate)?

when increasing TEMP

when DECREASING Ea

(activation energy is like speedbump —> low speed bump = car can drive over faster)

what factor has NO EFFECT on the rate constant (k)?

when you increase the [reactants]

equation for pH and pOH , and what their sum is?

pH = -log [H+] (aka [H+] = 10^-pH )

pOH = -log [OH-] (aka [OH-] = 10^-pOH )

pH + pOH = 14 (so if u incrs pH you decrs pOH)

eqn for pKa, pKb, and what their sum is?

pKa = -log Ka

pKb = -log Kb

pKa + pKb = 14

Henderson Hasselbach eqn?

pH = pKa + log[A-]/[HA]

K_water = ?

Kw = [H3O+][OH-] = 1x10-14

what happens to kb and pkb when you incrs the strength of a base? what about an acid?

incrs SB = incrs kb , decrs pkb

incrs SA = incrs ka, decr pka

relationship betweeen atomic radius and strength of H-bonds?

bigger the atomic radius = weaker the Hbonds = easier to dissociate = stronger acid !

name the 5 binary acids and order them from strongest to weakest acid?

HI > HBr > HCl >HF

what is conjugated acid + base?

CA = H+ added for bases

CB = H+ removed for acids

what are the two most common ways to make a buffer?

1) WA + Salt (CB) (ex: HF + NaF)

2) WA/WB + SA/SB

EQ Constant Expressions —> Kc

Kc = [products] / [reactants]

Rxn Quotient eqn

same as EQ

Q = [products] / [reactants]

• Q > K = shift left

• •Q < K = shift right

• Q = K = at eq

Standard Cell Potential eqn (E°]

E° = E°cathode - E°anode

Cell potenital and Gibbs Free Energy (combined eqn)

ΔG = -nFE

E > 0 = spont

E < 0 = nonspont

F = 96500 coulombs/mol

n = # mols of e’s transferred

speed of light

3 × 10^8

1 mol gas is how many L at STP?

22.4 L at STP

1 atm = mmHg = torr ?

1 atm = 760 mmHg = 760 torr

combining the Arrhenius, Bronsted-Lowry, and Lewis definitions of acids and bases

Acids: H⁺ producer, H⁺ donor, or an electron pair acceptor

Bases: OH^- producer, an H⁺ acceptor, or an electron pair donor