Adv. Chem Unit 7 - Entropy/Equilibrium

reversible reactions

reversible reactions

reactions that can take place in both directions

equilibrium

when the concentrations of the reactants and products stop changing

the rate of the forward reaction = the rate of the reverse reaction

at equilibrium, what is equal?

Keq = [C]ᶜ[D]ᵈ / [A]ᵃ[B]ᵇ

Keq Formula

(equilibrium concentrations)

equilibrium constant

favors the reactants

a small Keq indicates the reaction

favors the products

a large Keq indicates the reaction

take the reciprocal

if you reverse a reaction, you _______________ the Keq

raise the Keq to the x power

if you multiply a balanced chem equation by a coefficient of x, you __________________ the Keq

multiply

if you add two reactions together, you ________________ the Keq

Q = [C]ᶜ[D]ᵈ / [A]ᵃ[B]ᵇ

Q Formula

(initial concentrations)

reaction quotient

favors the forward direction

if Q > Keq, the reaction

favors the reverse direction

if Q < Keq, the reaction

has no direction affinity

if Q = Keq, the reaction

le chartelier's principle

states that if a system at equilibrium is disturbed by a change in temperature, pressure, or a component concentration, the system will shift its equilibrium position so as to counteract the effect of the disturbance

the solubility product (Ksp)

the degree to which dissolution occurs

Ksp = [A⁺]ᵃ[B⁻]ᵇ

the solubility product

low solubility

a small Ksp value indicates

high solubility

a large Ksp value indicates

molar solubility

molarity of a solute in a saturated solution (S)

common ion

an ion that is common to two or more ionic compounds

common ion effect

If one of the ions in a solution equilibrium is already dissolved in the solution, the equilibrium will shift to the left and the solubility of the salt will decrease

exothermic reaction

ΔH < 0

endothermic reaction

ΔH > 0

left

if you raise the temperature of a exothermic reaction, the reaction will shift to the

right

if you lower the temperature of a exothermic reaction, the reaction will shift to the

right

if you raise the temperature of a endothermic reaction, the reaction will shift to the

left

if you lower the temperature of a endothermic reaction, the reaction will shift to the

Equilibrium constant expression - Aqueous

Kc = [products]/[reactants]

Equilibrium constant expression - Pressure Only (g)

Kp = [products]/[reactants]

T/F - A <==> B Once equilibrium is established \[A\] = \[B\]

False

T/F - A <==> B Once Eq is established k forward = k reverse

True

T/F - A <==> B Once Eq is established the values of \[A\] & \[B\] are no longer changing

True

1 atm =

760 torr, 760 mmHg

Solids and liquids are

not in the Equilibrium constant

Forward reaction means:

Reactants to Products

Reverse reaction means:

Products to Reactants

Kc or Kp equation

Kc (or Kp) = [products]/[reactants]

Qc or Qp equation

Qc (or Qp) = [products]/[reactants]

Kc (or Kp) meaning

K gives the value of the reaction at Equilibrium

Qc (or Qp) meaning

Q gives the value of the reaction at any given time

Q compared to K

Q is compared to K to determine if the forward or reverse reaction are favored based on it being greater than, less than or equal to K

Q = K

Reaction is at equilibrium, neither the forward nor reverse reaction is favored

Q > K

Forward reaction (reactants to products) is favored / shifts to the left

Q < K

Reverse reaction is favored (products to reactants) / shifts to the right

Small K means

Because K = [products]/[reactants]

reactant number is bigger, because reactants are on the bottom and thus make a small number

Reactants are favored.

Bigger K means

Because K = [products]/[reactants]

product number is bigger, because product are on the top and thus make a larger number

Products are favored

Kp and Kc Units

No Units!

Le Chatelier's Principle

If a stress is imposed on a system at equilibrium the position of the equilibrium will shift in a direction that reduces that stress

LCP - Adding a product

shifts left (toward reactants)

LCP - Adding a reactant

shifts right (toward products)

LCP - Removing product

shifts right (toward products)

LCP - Removing reactant

shifts left (toward reactants)

LCP - Increasing volume

Shifts toward the side with more moles. This is similar to a decrease in pressure.

LCP - Decrease volume

Shifts toward the side with fewer moles. This is similar to an increase in pressure.

LCP - In an endothermic reaction, increasing temperature means...

Endo heat comes indoors, and is thus a reactant

so adding reactant, shifts right, the value of K increases because the concentration of the products increase and the concentration of the reactants decrease.

LCP - In an endothermic reaction, decreasing temperature means...

Endo heat comes indoors, and is thus a reactant

so removing reactant, shifts left, value of K decreases because the concentration of the products decrease and the concentration of the reactants increase.

LCP - In an exothermic reaction, increasing temperature means...

Exo heat exits and is thus a product so adding product, shifts left, value of K decreases because concentration of the products decrease and the concentration of reactants increase.

LCP - In a exothermic reaction, decreasing temperature means...

Exo heat exits and is thus a product so removing product, shifts right, value of K increases because the concentration of the products increase and the concentration of the reactants decrease.

LCP - Adding a catalyst...

Does NOT change the concentration

LCP - Adding an inert gas

Does NOT change the concentration

ΔH + then

Endothermic heat is a reactant

ΔH - then

Exothermic heat is a product

What happens to Kc in the reverse reaction?

The products become the reactants going backwards and the reactants are now products....

Kc = [reactants]/[products]

Kc equation

Catalyst as it relates to Equilibrium

has no effect on the position of equilibrium but lowers activation energy, increasing the rate of forward and reverse reactions(gets to equilibrium faster)

What happens to the value of K when flipping reactants and products?

becomes 1/K

K of reverse reaction

1/K original

Doubling K to equal an equation

original K squared

Halving K to equal an equation

original K to 1/2 power (sqrt of K)

Ksp

solubility product constant

Ksp=[A+]^m[B-]^n

Ksp equation

molar solubility

the solubility of a compound in units of moles per liter

Q<Ksp

precipitate forms

Q>Ksp

no precipitate forms

Two Factors Affect Solubility

pH and Common Ion Effect

Heterogeneous Equilibrium

equilibrium involving reactants and/or products in more than one phase

Homogeneous Equilibrium

a state of equilibrium that occurs when all the reactants and products of a reaction are in the same physical state

Phases used in Kc

aq and gas

Phases used in Kp

gas