Unit 7 - Chemical Equilibrium Flashcards
What are example of reversible changes?
Phase changes
Dissolution/Precipitation
Gas absorption/Desorption
forward reaction
Going from left to the right
reverse reaction
going from right to left
What occurs at equilibrium?
Rate of forward reaction is equal to the rate of reverse reaction
no net observable changes
Constant concentrations
Does concentration have to be equal?
Does not have to be equal
What does Equilibrium is DYNAMIC mean?
Continues to occur at same rates
In order for a net conversion to reactants to happen,…
The rate of the forward reaction has to be smaller than the rate of the reverse reaction.
Reverse reaction is favored
In order for a net conversion to products to happen…
The rate of the forward reaction has to be bigger than the rate of the reverse reaction
forward reaction is favored
When neither direction is favored…
EQUILIBRIUM
What is the reaction quotient?
Represent the relative quantities of products to reactants at any given point in time
what is the reaction quotient for aA +bB cC dD
[C]^c [D]^d / [A]^a [B]^b
What happens to the reaction quotient expression when used in gas phase reactions?
Instead of concentration, written in pressures
What phases are included in a reaction quotient?
Only gases and aqueous solutions
Solids and liquids are not
Can Qp and Qc be interchangeable?
NO
Qp does not and can not equal Qc
What is the equilibrium constant?
Same properties as the rxn quotient
Used instead during equilibrium
What does the value of Q indicate?
Whether the rxn will need to proceed towards the left or right in order to achieve equilibrium
What does the value of K indicate?
Whether there are more products or reactants at equilibrium
In order to calculate K is temperature needed?
Temp is NOT needed to calculate K
The numerator of Keq represents what
Products
The denominator of Keq represents what
Reactants
In a rxn favoring products, the Keq is
Larger
In a rxn favoring reactants, the Keq is
smaller
What does the magnitude of K tell us?
How the concentrations of reactants and products compare at equilibrium
K > 1 implies
[products] > [reactants]
K approx 1 implies
[products] is about the same as [reactants]
K < 1 implies
[products] < [reactants]
Can K be less than zero
NOPE
A SUPER BIG K value indicates
100% in forward and near 0 in reverse
Equivalent to complete forward
A SUPER SMALL K value indicates
0% in forward and 100% in reverse
Equivalent to complete reverse
What K values does a rxn need to have at equilibrium to proceeds significantly in both directions?
B/t 0.1 and 10
What is the coefficient rule?
When coefficients are changed by a factor of n, Keq is raised to the power of n
What is the reciprocal rule?
When a rxn is reversed the new Keq value is the inverse of the old Keq value
What is the multiple equilibria rule?
When two or more rxns are combined the new Keq is the product of the Keq values from individual rxns
If Q is larger than K
Numerator must decrease implies products must decrease
reverse rxn favored
If Q is smaller than K
Numerator must increase implies products must increase
forward rxn favored
What are the two sets of conditions as a rxn proceeds?
Initial conditions
Equilibrium conditions
what are the two methods of determining eq conditions given initial conditions and k
Neglect X
Perfect squares
What is the Neglect X method?
Only applicable when K is smaller than 0.0001
Remove x in the denominator
Negligible change and minimal effect
Once x has been determined, how can you use x to find the eq concentration.
Substitute value back into ICE table
ICE table
Initial
Change
Equilibrium
What is the perfect squares method?
Only applicable when both num and den are perfect squares
Simply Sqrt both sides and simplify
What does the LaChatelier principle state?
Changing rxn conditions of a system at eq can knock system out of eq causing stress
System will shift to reduce stress and achieve equilibrium again
What can be changed to stress a system?
Molarity
Pressure
Volume
Temperature
What happens with addition of reactants? decrease of products?
System will shift to consume reactants and produce products
What happens with addition of products? decrease of reactants?
System will shift to consume products and produce reactants
What happens when you dilute a solution?
Dilution causes all M to decrease/ rxn shift to side with greatest aq
Concentration a solution?
Concentration causes all M to increase/rxn shift to side with least aq
What happens in response to addition of a catalyst or solid?
No stress occur
What happens in response to increased pressure or decreased volume?
Rxn shift to side with least moles of gas
What happens in response to decreased pressure or increased volume?
Rxn shift to side with most moles of gas
Higher temp favor what kind of rxn
Endothermic
Lower temp favor what kind of rxn
Exothermic
what happens to the K value in endo rxn
K new > K old
What happens to K value in exo rxn
K old > K new
If Q = to K then
equilibrium
Keq only changes if
Temperature changes
What is solutibility?
Denoted as S
Amount of a salt that will dissolve to form a saturated solution at a given temp
Salts classified as insoluble are actually…
Slightly soluble
Ksp
is the K for solutibility product
Solubility constant in an 1:1 ion ratio is…
Ksp = S^2
Solubility constant in an 1:2 ion ratio is…
Ksp =4S^3
Solubility constant in an 1:3 ion ratio is…
Ksp =27S^4
Solubility constant in an 2:3 ion ratio is…
Ksp =108S^5
In order to calculate S
Set S equal to Ksp and simplify
Presence of some solid in a rxn…
provides evidence that a solution is saturated
Solubility is expressed in…
g/L or mol/L
Soluble salts has a Ksp of….
> 1
In order to compare the solubility of insoluble salts
Compare the S value
Ksp can only be compared when…
Both salts have the same ion ratio
The Qsp can be calculated with..
any or initial ion concentration
The Ksp can be calculated with…
eq ion concentration
If Ksp > Qsp, then a precipitate…
Will not form
Not enough ions and unsaturated solution
If Ksp < Qsp, then a precipitate…
Will form
Saturated solution
What is the common ion effect?
a common ion causes decreased solubility
How to calculate S when a common ion is present
Use ICE Table
S is negligible in eq concentration + S
Set Ksp equivalent to S
What is a neutralization rxn?
Acid +Base –> Water and Salt`
Solubility of a class of slightly soluble compounds that contain hydroxide or conjugate base of a weak acid
Is highly sensitive to addition of acids or bases