chapter 12: chemical equilibrium Flashcards
what is a reversible process
processes that proceed in a forward and reverse reactions
as the forward reaction slows that happens to the reverse reaction
it speeds up
what is a dynamic equilibrium
a condition where rates of forward and reverse are equal
what is chemical equilibrium
opposing reactions are proceeding @ equal rates
- conc. are constant bc react are being consumed and made at the same time
is dynamic equilibrium the same as chemical equilibrium
yes, they mean the same thing
in equilibrium are concentrations equal
no conc. are not equal but their rates are
what is the law of mass action
rates of forward and reverse reactions are equal but NOT in concentration
- ratio of rate is a constant as long as the TEMP remains constant
who discovered the law of mass action
-cato guldberg and peter waage
What is Kc
Kc is the equilibrium constant
- [prod]/[react]
- unitless
what do you do in the Kc expression if you have an ion
- include the ion outside of the []
when manipulating Kc what are the rules for when it has
- ) flipped
- ) there is a coefficient
- ) adding them
- ) if it has flipped find the inverse of k or 1/K
- ) multiply coefficients by the factor n 2c = [c]^2
- ) multiply them together to add them
what is the relationship between Kc and Kp
- the concentration of gas is proportional to its Partial pressure
when does Kc = Kp
when the change in moles is equal to 0
what are homogenous and heterogeneous equilibrium
- homogenous means the same phase
- heterogeneous means different phases
what types of phases do we calculate K for
- gases and aqueous
why do we not use solids or liquids to calculate equilibrium
- pure solids and liquids do not change significantly during the reaction and they do not change their concentration
what are the 3 applications of K
- ) whether a given set of [] represents equilibrium
- tendency of reaction to occur
- equilibrium position that is achieved from the initial concentration
are K and time related
no, they are not
what does it mean when…
- K is more than 1
- K is LESS than 1
- if K is more than 1 that means it is the product favored ( more prod. than react.0
- if K is less than 1 then it is reactant favored (more react. than prod)
what happens if one of the reactants or products is zero
the system will shift to produce/ replace the missing component
what does Qc tell us and what is it
the direction a reaction will proceed
Q is the same thing where you have to substitute Kc or Kp for Qc and Kc
Q= k
@ equilibrium NO shift
Q < K
the reaction will move FORWARD (towards the products)
- as rxn approaches equilibrium, the products will increase and react. will decrease
-
Q > k
the reaction will proceed in the REVERSE direction
- as rxn approaches equ. products will decrease and reactants will increase
what do method do you need to use when calculating Kc when once equilibrium concentration is known
ICE Table
- I: initial
- C: Change in concentrations
E: equilibrium concentrations
when one equilibrium concentration is known what steps do you usually do to get the right answer
1.) tabulate all the formulas and whenever you put the equ. conc. then make sure to put the difference in the change, also look at the number of moles to determine the change.
how do you determine the equilibrium concentrations from initial concentrations
- ) use X in the places of what the change is
- ) if nothing is initially present use 0
- ) when given the Kc and you’re trying to find x if Kc is <<1 and is super small then ignore the x (0.3289-x) but if Kc is large then use the x and use the quadratic formula
if you have (1.000-x)^2 in the denominator then what should you do
foil the denominator into (1.000-x)(1.000-x) then distribute if there was another coefficient in the front
when do we use approximations
when Kc is very small and it favors the reactants
what is the 5% approximation?
what is the equation?
approximate x/ initial conc. x100 <5%
if it less than 5% then it is valid,
if it is more than 5% then it is not valid
what is Le Chatelier’s principle
- stated by the french chemist Henri-Louis Le chatelier
- system @ equi. is disturbed by a change in temp, pressure or the conc. of one of the species, the system will shift its equilibrium position so as to counteract the effect of the disturbance
what are the steps of le chateliers principle
- system starts at equil.
- change is made to the system in one of five areas
- the system responds by shifting to the right or left to restore equilibrium
* here we are specifically talking about a forward reaction*
what are the 5 different areas that can make equilibrium change
- concentration
- volume
- pressure
- temperature
- catalyst
effect of concentration changes
what happens when you add a substance to the reactant side or product side? In what way will it shift
- add to the reactant side: more reactants than products so it will shift to the products to reestablish equilibrium ( forward reaction)
- add the product: more product = shift to the reactants to reestablish equilibrium (reverse reaction)
what has no effect on the concentration and on equilibrium
solids and liquids
initially adding a reactant does what to the rate of the forward reaction and reverse reaction
- increases the rate of the forward and it doesn’t affect the rate of the reverse
- at equilibrium you will have more products and less of the non-added reactants because they are getting consumed
- new equilibrium the Kc(new) = kc (initial)
what does removing a substance do
cause the reaction to move in the direction that forms more of what was removed
- removing a reactant = increase the reactants = reverse
- removing a product = increase the product = forward
what does le chatleliers principle say about pressure and volume
- volume decreased, pressure increased= system will respond by shifting to reduce the pressure( going to the side with lower moles)
- volume increased, pressure decreased= system will respond to increase pressure( go to the side with higher moles)
changing the size (volume) of the solution doesn’t affect what
solids, liquids, and solutions
it only affects gases
what happens if you add a gaseous reactant
it will increase the pressure and shift to the right
do noble gases have an effect on equilibrium, if no why not
- noble gases don’t have an effect on equilibrium
because noble gases on the period table are already stable so they are intent and unreactive
if a reaction is endothermic and you increase the temperature what way will the reaction shift, what will happen if you decrease the temperature
heat + A + B —> C + D
- ) endothermic + increase temp = increase reactants means to shift to the products to reestablish
- ) decrease heat = taking away heat = shift to the reactants = reverse reaction
if a reaction is exothermic and you increase the temperature what way will the reaction shift, what will happen if you decrease the temperature
A+ B = C+ D + heat
exothermic = heat is a product
- increase heat = more products = shift to the reactants = reverse reaction
- decrease heat = take away a product = shift to the products to replace = forward reaction
what does a catalyst do
- decreasing the activation energy
- increase the rate of both forward and reverse reactions by the same factor
- do NOT affect the position of the equilibrium
