chem 2 equilibria

equilibrium

state in which there are no observable changes as time goes by (ratefwd=ratervs)

chemical equilibria

the rates of the fwd + rvs reactions are equal + the conc of the reactants and products remain constant

dynamic equilibria

both fwd + rvs rxn are occurring - no net concentration change

what is important for equilbria?

rates are equal , concentrations are unequal but constant

reaction quotient

measures the relative amounts of p + r present during a reaction at a particluar point in time (P/R raised to stio. power)

law of mass action

for a chemical reaction mixture that is in equilibrium, the ratio between the conc of p + r is constant for a reaction at equilibrium, K is constant for a specific temp

K » 1

lies to rights - larger numerator - favors products

K« 1

lies to right - larger denominator - favors reactants

Qc < Kc

Qc must increase

• need more product —>

Qc>Kc

Qc must decrease

• need more reactant ←

examples of stress

• addition/removal of r/p

• volume change

  • r/p presssures change

  • t change

important for changes in v/p

Q (+K) don’t change, BUT equilibrium may shift

no effect if delta gas = 0 (equilibrium cannot adjust)

adding a non-reacting gas at constant V has no effect

• total P increases but V, n_reactants and n_products are unchanged

• concentrations are unchanged

volume decreases

each gas increases in P_partial (total P increases )

volume increases

each gas decreases in P_partial (total P decreases )

changes in V,P,{} don’t change ___

K

a change in T will change in ___

Kc

endothermic

• heat is a reactant

• increases temp

• response: remove heat

• shift —>

• Qc increases to reach Kc

catalyst

speed up both reactions

• no change in K - just reaching it faster

acid

subst that produces H+ in water

base

subst that produces OH- in water

acid is a proton ___

donor

base is a proton ___

acceptor

2 species which differ by a single H+ are ____

conjugates

amphiprotic compounds

can donate + accept protons

kw is ___ dependant

temp

strong acids

HCl, HBr, HI, HNO3, H2SO4, HClO4

strong bases

LIOH, NaOH, KOH, RbOH, CsOH, Be(OH)2, Mg(OH)2, Ca(OH)2, Ba(OH)2, Sr(OH)2

stronger acid the ____ the ka

larger

weak acid :

weak conjugate base

strong acid :

neutral ion as conjugate base

nuetral ions in solutions:

all strong conjugates

kb > ka

basic solution

ka>kb

acidic solution

ka=kb

neutral solution

when a reaction is reveresed the new k is ?

found from the inverse of k

kw will not change at same temp so if [H3O+] increases —-

[OH-] decreases

stronger acid = more ___ = larger ___= making more ___

[H30+], Ka, product

strong bases include ____

group 1 + 2 hydroxides (NOT BE)

[H3O]increases % I ___

decreases ; in a mixture of acids w/sim concentrations - diff Ka = weaker acid has no impact on pH

the small x approximation works when the fraction ionized is ___

< 5%

organic acids

contain the carboxylic acid functional group

amine

any hydrocarbon (-CH3) + lone pair on N accepts a proton

salt hydrolisis

ions react with water to produce OH ±H3O

strong acid + strong base —>

neutral salt + water

conjugates of strong acids/bases -

dont hydrolyze with water

strong acid + weak base —>

acidic salt

weak acid + strong base —>

basic salt + water

weak acid + weak base —>

? salt + water

• both components of the salt react with water (both are conjugates of weak acid/base)

many 1st row transition metals are:

acidic

acidic cations

conjugate to weak base - small high-charge metal (not 1a/2a)

basic anions

conjugate to weak acid

neutral cations

group 1A / heavy group 2A

neutral anions

conjugate bases of strong acids

polyprotic acids

H2S, H3PO4, H2CO3, HOOC-COOH, C3H5(COOH)3

buffers

resist a change in pH when a small amount of strong base/strong acid is added (prepared by mixing a conjugate pair)

henderson hasselbach equation

pH= pKa +log([Ai]/[HAi])

important in acid/base reactions

• neutralize eachother

• # of mols by stoichiometry

• smaller amount - will be wiped out

steps for acid-base titrations:

1. choose reaction type (strong-strong/strong-weak)

2. calc molar changes (LR)

3. calc pH after reaction

   1. any strong (H3O/OH) remains

   2. ‘weak’ pair present (h.h.)

   3. only one ‘weak’ present

if mole sOH- wiped out —>

ICE +h.h. excess moles OH- —> pOH directly

in acid-base titrations where does pH=pKa

half-way