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)
