TEST 3: 13, 14.1-14.6, 17.8-17.9 Flashcards
If Kc is much less than one it favors
reactants
If Kc favors reactants
equilibrium shift to the left
Q>K
products>reactants, reactant favored, shift left
Q<K
reactants>products, product favored, shift right
When a reaction is product favored the shift will cause
concentration of products to increase and reactants to decrease
Homogeneous equilibrium
in the same phase, excludes concentration of pure solids and liquids
Heterogeneous equilibrium
not in the same phase, excludes concentration of pure solids and liquids
In a reactant favored reaction, the rate of the forward
is slower than rate of reverse
A reaction will proceed forward
when Q<K, reactants converted to products
A reaction will proceed in the reverse
when Q>K, products converted to reactants
K»1
product favored
K«1
reactants favored
If Q<K gibbs free energy
is negative regardless of gibbs under standard conditions
What causes a change in Gibbs free energy to shift with equilbrium?
A concentration-gradient reflected in the fact that the change in entropy under non-standard conditions is not the change in entropy under standard conditions–remember the natural tendency to disperse evenly throughout a system
Change in instantaneous gibbs free energy that is positive
Q>K
Negative change in instantaneous gibbs free energy
reaction is not at equilibrium
When standard conditions are restored from equilibrium, the value of Q progressively decreases. This must mean that we have
standard change in gibbs free energy that is negative
Reversible reactions do not
go to completion
At equilibrium
no net change in concentration, rate forward = rate reverse, these reactions do not stop
A reaction will essentially go to completion if
K > 10^10
A reaction will essentially not occur if
K < 10^-10
What are not included in equilibrium constant expressions
solids and liquid
Kc does not depend on
initial concentrations
Kc changes when
temperature changes, directly related
Things to check when doing equilibrium constant calculations
Is it balanced? Are there solids or liquids? Are equilibrium concentrations given and not initial concentrations?
When volume is decreased
pressure increases and reaction shifts to less gas
La Chatelier
system changes rates
Shift right will cause
increase reactants, decrease products, rate forward increase
Shift left will cause
decrease reactants, increase products, rate reverse increase
Decrease pressure
shift right
Consider heat
reactant in endothermic, product in exo
Add heat in exo
shift left, heat added to products and temp increased
Add heat in endo
shift right, heat added to reactants
Equation free energy and Kq
delta G°= -RTlnK
R in delta G° equation
0.008314 kJ / mol
ΔG° < 0
K>1, products
ΔG° > 0
K< 1, reactants
Equation relating Q and free energy
ΔG = ΔG° + RTlnQ
ΔG = -RTlnK + RTlnQ
ΔG < 0
K > Q, products
ΔG > 0
K < Q, reactants
PH =
-log[H+]
Increasing Ka
increasing acidity
When the concentration of hydroxide ions is. less than hydronium ions
acidic
How to find the concentration of hydronium ions from hydroxide ions?
(1.0x10^-14) / given concentration
Hydronium ion
H3O+ ion, a hydrated proton
Conjugate base
everything that remains of the acid molecule after a proton is lost
Conjugate acid
formed when the proton is transferred to the base
Ka equation
[H3O+] [A-] / [HA]
Acid dissolved in water equation:
HA (aq) + H2O (l) -> H3O+ (aq) + A- (aq)
Ka definition
association dissociation constnat
Strong acid
equilibrium lies far to the right, almost all HA ionized
What do strong acids yield
a weak conjugate base (low proton affinity)
Weak acid
equilibrium lies far to the right, dissociates only to a very small extent
Weak acid is a conjugate base that is
much strong base than water
Oxyacids
weak acid, phosphoric acid, nitrious acid, hypochlorous acid
Organic acids
carbon atom backbone, contain carboxyl group, usually weak
Organic acid examples
acetic acid, benzoic acid
Autoionization of water equation
2H2O (l) -> H3O+ (aq) + OH- (aq)
Kw equation
[H3O+] [OH-] = [H+] [OH-]
in pH [H+] =
1.0 x 10^-7 <
Arrhenius Acid
contain hydrogen and increase H+ ion concentration in solutions
Arrhenius Base
contain hydroxide and increase OH- concentration in solutions
Bronsted-Lowry acid
donates proton H+ to some accepting species
Bronsted-Lowry base
chemical species accepts proton H+ from donating species
Bronsted-Lowry equation
reactions are reversible, acids on one side can be a base on the other side
All acids or bases can be classified
as lewis acids or bases
Conjugate acid and base
acids and bases ionize and separate from their protons or hydroxides and leave behind these
Water acts as an
amphoteric, can be acid or base, frequent conjugate of both acids and bases
Water ionization constant Kw
= 1.o x 10^-14 at 25 degrees
If H3O+ concentration is higher than OH-
solution is an acid
pH for H3O+
-log[H3O+]
pH for OH-
-log[OH-]
[H3O+] related to pH
10^-pH
A Ka and Kb much greater than one
strong acid or base
A high PKa and PKb show
a low percentage ionization
A low PKa and PKb show
a high percentage ionization
PKa and PKb =
-log
Strong Acids phrase
So I BRough No CLean CLOthes
Strong Bases Remember
metal cations in group 1 (without Fr), and heavy group 2 metals (without Ra)
If acid concentration is more an 100 x Ka
“X” in HA-X can be ignored
Standard Free energy
tells whether product or reactant favored
Change in free energy
to reach equilibrium how will the reaction have to shift
ΔG° compares
G to 0 and K to 1
ΔG compares
Q to K
Degree of ionization a
a = [Molarity of the Conjugate Base of HA] / [Initial Molarity of HA]
a = [Molarity of Conjugate Base of HB] / [Initial Molarity of B]
Percent ionization =
a x 100
For weak acids, percent ionization increases with
increasing dilution
Strong acids and bases degree of ionization =
100%
Stronger the acid
weaker conjugate base
Large Kb
Small Ka
strong base
weak conjugate acid
Small Kb
Large Ka
weak base
strong conjugate acid
Small Kb
Large Ka
weak base
strong conjugate aci
Use Ka or Kb for acid and base to find X
Ka
Which are ignored for strong bases
Na+ and K+
Which are ignored for strong acids
Cl- and NO3-
When are strong acids and water ionized
Strong acids completely ionize first and then water
When H3O+ concentration > OH- concentration
Acidic
A large pKa
weak acid, pH is still acidic
When finding overall Kc, the Kc of each reaction
MULTIPLIED not added
Adding inert gas at constant pressure
shift to side with more moles of gas
Adding inert gas at constant volume
no effect
Percent dissociation
amount dissociated / initial concentration x100%
All acid base reactions favor
direction where strong acid or base react to form weaker acid or base
Strong acid with strong base
Large equilibrium constant, water and neutral salt as product, neutral effect on solution
Strong acid with weak base
Large equilibrium constant, water and acidic salt as products, acidic effect on solution
Weak acid with strong base
Large equilibrium constant, water and basic salt as products, basic effect on solution
Weak acid with weak base
Small equilibrium constant, water and salt as products whose pH depends on strength of conj acid and base present, effect on solution depends on pH
pH and temperature
inversely proportional
Kw and temperature
directly proportional
Strong acids completely dissociate so
given M you know that -log will be pH
If a base or acid is % dissociated (in ICE chart)
the % x M is the Change in ICE table
The conjugate of a strong acid
is a very weak base
K value increase or decrease with increase in temperature
decrease (does not change with P or V)
Amphoteric example
HPO4 2-
As temperature and Q increase, how does G change
increases
