HC Chem. ch.12, 13 & 16,17 (IMF & Sol'n & kinetics/equilibrium)

What factors affect rate?

1. Concentration (more collisions!) 2. Pressure (inc. P = inc. conc.) 3. Temperature (inc. T = inc. rate) 4. Catalysts (decreases Ea) 5. Surface Area (heterogeneous rxns) -diff physical states!

Inter Molecular Forces (IMF)

1. Dispersion forces (instant dipole-induced dipole) 2. Ion-dipole 3. Dipole-dipole 4. Hydrogen bond

Calculating K of A/B rxns

1. Hydrolysis rxns for WEAK A/B 2. Add SA + SB neutralization (H3O+ + OH- -> 2H2O) 3. Add rxns up & multiply K's K = Ka X Kb / Kw

Shortcuts for identifying IMF!

1. Ion-dipole is only for (aq) & salt cmpds 2. H only bonds to FON! 3. everything has london dispersion 4. H2O has dipole-dipole too! 5. Cmpd in H2O, cmpd has to have FON in order to have H-bonding the relevant IMF!

3 kinds of rxns for K values

1. Product favored = K>>1 2. Reactant favored = K<<1 3. Reversible = K~1 (.001<K<1000)?

Group 1 & 2 Metals ARE NOT _____

ACIDIC!

Intrinsic reactivity

Acid + Base = fast Ar + HF = slow

Arrehnius

Acid = H3O+ in sol'n Base = OH- in sol'n

Lewis

Acid = e- pair acceptor Base = e- pair donor

Acid vs. Base charges

Acids = usually nuetral or positive charged Bases = usually neg. charged except ammonia (NH3)

Fe(H2O)6^3+ rxn (always 6!)

Fe(H2O)6^+3 + H2O -> H3O+ + Fe(OH)(H2O)5^+2 *add H2O for these rxns* -For every metal in a ionic cmpd that aren't Group 1 or 2 metals!

If you have a strong acid/base, your conjugate acid/base will be____

the same as you! If strong acid, your conj. base is still an acid!

rate determining step

the slowest elementary step which is the limit for the rate of the other steps

If _____ then ∆H sol'n = endo or exo

∆ H1/∆ H2 > ∆ H3 then ∆ H sol'n = + ∆ H1/∆ H2 < ∆ H3 then ∆ H sol'n = -

Equation for energy changes

∆H hydration + ∆H lattice = ∆H sol'n

∆H's defined

∆H1 = strength of A ∆H2 = strength of B A & B = cohesive forces ∆H3 = strength of A-B (adhesive forces)

How to make a slow rxn fast:

*effective w/ all 3 combined!* 1. Heat it = speeds it up but pushes it back/rev 2. Catalyst = doesn't shift to prod tho! -both forward & reverse rxns speed up -no change in EQ [ ]'s! 2. Compress it

london dispersion forces

*everywhere* weak intermolecular forces responsible for the attraction between nonpolar molecules

Polyprotic A/B's

*less H's = stronger acid & more H's = stronger base* HC2O4 is "amphoteric" For pH calcs, only use 1st hydrolysis step!

Kinetics

*mechanism* -series of ind. rxn steps that constitute an overall net process -each step=elementary rxn

ion-dipole forces

*only for aq sol'ns* attractive forces between an ion and a polar molecule

Boiling Point vs. IMF

*weaker IMF=lower BP* greater polarity=higher BP more surface area=higher BP

Trend of strength for Carboxylic Acids

*~COOH* 1. If F is present, it's the strongest acid 2. More bonds = weaker acid

pH

1-7 Acidic 7-15 Basic pH=7 Neutral

Steps for strongest IMF between solute & solvent

1. Check formula of solute & solvent & identify IMF's 2. Determine if forces would occur 3. Ionic forces=ionic cmpds, dipole-dipole forces=polar cmpds, dispersion forces in non-polar cmpds 4. ion-dipole>H-bond>dipole-dipole> ion-induced dipole>dipole-induced dipole>dispersion

Covalent bond

A chemical bond that involves sharing a pair of electrons between atoms in a molecule

Energy changes w/ making a sol'n

A(s)/(l) + B(s)(l) -> AB(mix) ∆ H1 = break up "A" = + ∆ H2 = break up "B" = + ∆ H3 = A-B(solute/solvent interactions)= - ∆ H sol'n = ∆ H1 + ∆ H2 + ∆ H3

Activation energy

*always +* Ea kJ/mol the minimum quantity of energy that the reacting species must possess in order to undergo a specified reaction.

Bronsted/Lowry

*always a rxn* Acid = H+ donor Base = H+ acceptor

Hydrolysis

*chemical breakdown of a cmpd with water* -product favored

Trend of strength for oxo-acids

(HNO3) More O's = stronger acid *more electronegative*

Weak Acids

*H3O+ > WA > H2O* 1. H + a common ion 2. Organic acids: ~COOH (no alcohols) 3. Ammonium NH4+ 4. Metal ions: not Group 1 or 2!

Trend of strength for Binary Hydrides

*HA - single element* 1. Follows trend of ENG: more ENG = weaker acid 2. Strength of A/B increases down a group

Strength of IMF's

*IHDD* dispersion < dipole-dipole < hydrogen bond < ion-dipole

Weak Bases

*OH- > WB > H2O* All anions are WB except conjugate bases of strong acids! Ammonia NH3

Volatility

*Tendency to vaporize* At given T, a substance with higher vapor pressure vaporizes more readily than a substance with a lower vapor pressure.

H-bond strength trends

1. Strength increases w/ polarity of H-bond in "donor" F-H>O-H>N-H 2. Vice versa for "acceptor" atoms N>O>F

4 types of ionic cmpds/salts (match them): 1. cation is acidic a. KCl 2. anion is basic b. NaNO2 3. neither c. NH4NO3 4. both d. NH4CN

1. cation is acidic - c. NH3NO3 2. anion is basic - b. NaNO2 3. Neither - a. KCl (K+ is GP1, Cl- is CB of HCl so still an acid!) 4. Both - d. NH4CN (basic overall cuz Ka<Kb)

1. 1st order, [A] doubles, then rate ____ 2. 2nd order, [A] halved, rate ____ 3. 2nd order, [A], quadrupled, rate ___

1. doubles 2. decreases by a factor of 4: (1/2)^2 3. increases by a factor of 16!

Intramolecular forces

1. ionic bond (cation-anion) 2. Covalent bond

Kw Constant =

10^-14

pOH + pH =

14

Units for k for overall rxn order

1st = s^-1 2nd = m^-1 s^-1 3rd = m^-2 s^-1

Hydrogen bond

Attraction between a slightly positive hydrogen atom and a slightly negative atom.

Ionic bonding

Chemical bonding that results from the electrical attraction between cations and anions

Autoionization

process by which an atom or a molecule in an excited state spontaneously emits one of the outer-shell electrons, thus going from a state with charge Z to a state with charge Z + 1

Solids don't affect ____ for Le'chatlier's principles.

Equilibrium so no shift if solids are added or removed for a rxn!

Strongest IMF for C6H14 in C8H18

Dispersion *both non-polar cuz of C-H bonds!*

What force predominate & most affect boiling pt. & delta H vap?

Dispersion when given data (#'s)

Surface Area

Hydrocarbon single chain = more SA & high BP Hydrocarbon (square?) chain = less SA & low BP

H2O forms H bonds, why doesn't H2SE?

Hydrogen bonds needs the atom bonded to the H to be small & very electronegative (need high e- density). O is smaller & more elctro. than SE! EX: N,O,F good

k

rate constant determine by doing k = rate/[A]^m[B]^n

Group 7A (size vs. BP)

smallest elements have the lowest BP!

Conjugate See-Saw

Inverse relationship between Base to CA & Acid to CB! EX: a stronger but still weak acid would have a weak conj. base

Products are favored when

K is over 100/1000

Reactants are favored when

K is under 100/1000 anything to the 10^1#

Q vs. K

K=equil. constant Q=constant not necessarily at equil. Q<K rxn will go forward (prod) Q>K rxn will go back (react) Q=K at equil. so rxn doesn't go anywhere!

Ka/Kb values for strong A/B

Ka (H3O+) = 1 Kb (OH-) = 1 Ka for strong acid > 1 Kb for strong base > 1

Kw =

Kb x Ka

Kc

Keq for concentrations *prod. & Kc have linear relationship* *reacts & Kc have inverse relationship*

Rule for Q & K eqn's!

LEAVE SOLIDS AND LIQUIDS OUT OF EQ'N!

Strength of acids

Less - charge = stronger acid More H = stronger acid

Solution

Mix 2 things (equal parts)

Strength of Bases

More - charge = stronger base Less H = stronger base

∆H hydr.

Na+(g) + Cl-(g)->Na+(aq) + Cl-(aq) ∆H hydr. = -784kJ *(∆H:1) Make few pockets in H2O (~∆H1) Make ion-dipole forces (∆H3)*

∆H Sol'n

NaCl(s) --> Na+(aq) + Cl-(aq) ∆H sol'n = 4kJ NaCl(s) = break ionic bonds NaCl(aq) = ion-dipole forces

∆H lattice

NaCl(s) -> Na+(g) + Cl-(g) ∆H lat. = +788kJ *∆H to break ionic bonds ~ ∆H1*

To determine a rate law

Rate ratios & differences in concs. -if finding exponential # for reactant [A], use concs. that differ for [A] but stay the same for all other reactants!

Equilibrium

opposing rxns @ equal rates -dynamic cuz reacts. continue to form products but at same rate that products decompose to re-form reacts.

Chemical Kinetics

Study of rxn rates 1. Practical reasons 2. How fast for mechanisms

Polarity

permanent imbalance in e- distribution in the molecule. Affect dipole-dipole!

Strongest dipole-dipole forces is determined by ____

polarity

Ka/Kb values for weak A/B

Weak Acid: 10^-14 < Ka < 1 Weak Base: 10^-14 < Kb < 1

Eq'n of lnk vs. 1/T graph

lnk = (-Ea/R) * (1/T) + lnA y = m * x + b

Keq

[products]^x/[reactants]^y x & y = powers of rxn coefficients *NO UNITS* Kc=concentrations Kp=partial pressure (at gas phase)

Polarizibility

ability of e- distribution in a molecule to change temporarily. -Affects dispersion forces! -trend=same at atomic size

Strongest dispersion forces is determined by ____

atomic size -linear relationship

Dipole-dipole forces

attractions between oppositely charged regions of polar molecules

Reaction Rate

change in concentration of reactants or products per unit of time

Temp vs. k

curves up

determine strength: HI, HCl, HBr

dipole-dipole & dispersion *look at size!* HCl<HBr<HI

bonds vs. polarizibility

e-'s in pi bonds are more easily polarized than e-'s in sigma bonds

Rate Law

equation that quantifies rate (especially concentration dependence) *Rate=k[A]^m[B]^n*

O-H part

hydrophilic *more = more soluble in water*

C-H part of hydrocarbon

hydrophobic *more of these=less soluble in water*

How can a non-polar molecule induce a dipole in a nearby non-polar molecule?

if e- distribution in one molecule is not symmetrical (permanent or temporary), that can induce a temporary dipole in an adjacent molecule by causing the electrons in that molecule to shift for some (often short) time.

Reaction w/ given Ea; increase T & rate ___

increases

Reaction w/ given T; increase Ea & rate ___

increases *lower energy threshold for collisions needed*

Strongest IMF for CsCL(s) in H2O(l)

ion-dipole Cuz CsCl(s) in H2O dissolves into ions!

k=Ae^-Ea/RT

k=rate constant T=temp R=gas constant (8.314 J/K*mol) Ea=activation energy A=pre-exponential factor *inverse relationship between k & Ea*

delta H vap vs. IMF

linear relationship -inc. Hvap = stronger IMF

Usable form of eq'n

ln k2/k1 = (-Ea/R)*(1/T2 - 1/T1)