Exam 3 Flashcards
Lectures 27-35
equilbirum
rate fwd = rate rev
* appears to be no change occuring
* collisions still occuring
dynamic equilbirum
rate fwd = rate rev
chemicals are consumed and made at the same rate, not necessarily the same concentration
equilbrium favors products
rxns that reach equilbirum after almost all reactant molecules are consumed
equilibrium favors reactants
rxns that reach equilbirum after a small percentage of reactant molecules are consumed
equilibrium systems are ___ and ___
dynamic
reversible
what 2 factors do not change at equilbrium in a closed system
concentration and pressure
law of mass action
if the system is at eq. at a given temp, then the ratio of product concentration and reactant concentration is constant
* k or kc
eq constant for rxns with gases
can be expressed as the ratio of the partial pressures of the gasses
which states of matter are not included in the expression of the eq constant
solids and liquids
why are solids and liquids not included in Q and k equations
their [ ] are constant
if keq = a very large number…
there is way more product than reactant
if keq = a very small number…
way more reactant than product
reaction quotient
ratio of [ ]s and/or pressures of the products and reactants in a mixture that may or may not be at equilbirum
which way does the system need to shift when Qc<Kc
right
which way does the system need to shift when Qc>Kc
left
difference between Qc and Kc
Qc is at any time during the reaction
Kc is at eq
for endothermic rxns, is heat a product or reactant
reactant
for exothermic rxns, is heat a reactant or product
product
relationship between pressure and volume
inverse
what 2 conditions regarding gases have no effect on eq
- inert gases
- moles of gas particles are equal on both sides
how does adding a catalyst effect eq and k
it does not, just makes system reach eq faster
La Chatelier’s Principle
whenever you force a change on a system at eq, the system will move ina way to undo that change
intert gas
noble gas
partial pressure
pressure exerterted by an individual gas in a mixture
relationship between partial pressure and concentration
direct
given k, what is k’ if the second equation is
1. doubled
2. halved
3. flipped
- k^2=k’
- k^1/2=k’
- 1/k=k’
when do you make an ICE table
when the Molarity is not at eq
remember
- for kc, if both the numerator and denominator are squared, square root both sides of equation rather than expanding it
when can you use the 5% or 400 rule
when kc<=a numberx10^-4
5% rule
if (x/number before the -x)*100<=5
what do you do if kc is not a very small number
quadratic formula
after the quadratic formula, how do you know which x is correct
the x that’s not negative
* if both are positive, it’s the x that’s less than the starting amount of molarity
Arrhenius Theory (must be in water)
- acid: has H+, dissociates in H2O to form H3O+ and negative ions
- base: has OH group, dissociates in H2O to form OH- and positive ions
Bronsted-Lowry Theory
- acid: proton donor
- base: proton acceptor (doesn’t need OH, has lone pair to accept H+)
Lewis Theory
- acid: accepts an electron pair (doesn’t need to have hydrogen)
- base: donates an electron pair (doesn’t need to have an OH)
base
nucleophile: electron-rich
acid
electrophile: electron-poor
___ dissolve fully in water
salts
monoprotic acid
can donate 1 H+
diprotic acid
cane donate 2 H+
polyprotic acid
can donate >1 H+
Steps for ICE table
- write balanced eq
- ICE table
- write ka equation and plug in values from E of ICE
- set equal to ka value given
- use 5% or 400 rule
- solve for x
- use x to find whatever the question asks for (pH or eq [ ])
buffer
when present in solutions, they prevent dramatic changes in pH when an acid or base is added
what is a buffer made out of
- weak acid and its conjugate base with a salt
- weak base and its conjugate acid with a salt
log sig fig rules
sig figs in answer after decimal point is the same number of sig figs in log
* in other words, sigs figs of number inside log() is the number of sig figs after the decimal point in the answer
ex. log 4.000 (4 s.f.) = 0.6021(4 s.f. to right of the decimal point)
buffering capacity
amount of acid or base a buffer can neutralize
when is the higher buffering capacity
[A-]=[HA] b/c pH=pka+log([A-]/[HA])
buffering range
pH range the bugger can be effective
when choosing an acid to make a buffer, which one do you pick
acid whose pka is closest to the pH of the bugger
what equation do you use to calculate the pH of a buffer
henderson-hasselbalch
inert gas
noble gas
when does kp=kc
when the number of moles of products and reactants are equal
b/c kp=kc(RT)^n
order of proton removal in amino acids
acidic - COOH, R-group, amino group
basic - COOH, amino group, R-group
neutral - COOH, amino
