Chem II - Equilibrium

Keq and Q equation

[C]^c[D]^d/[A]^a[B]^b

Keq > 1

Product favored (at eq. more product is formed)

Keq < 1

Reactant favored (at eq. more reactant is formed)

Keq = 1

Reaction is neither product nor reactant favored (equal amount)

Keq > 10¹⁰

Reaction goes to completion (irreversible)

Keq < 10^-10

Reaction does not take place

Increase in temperature (kinetics)

Increase in rate

Increase in concentration (kinetics)

Increase in rate

Catalyst (lower activation energy)

Increase in rate

Increase in pressure (kinetics)

Increase in rate

Increase in volume (kinetics)

Decrease in rate

Zero order

If the concentration of A changes, the rate does not change

First order

If the concentration of A changes, the rate changes the same amount (directly proportional)

Second order

Rate is directly proportional to the squared concentration of A

Le Chatelier's principle

If a reaction at eq. is disturbed, the reaction will shift to cancel the disturbance until eq. is reached again

Add heat to an exothermic reaction

Reaction shifts left

Remove heat from an exothermic reaction

Reaction shifts right

Add heat to an endothermic reaction

Reaction shifts right

Remove heat from an endothermic reaction

Reaction shifts left

Increase in pressure (Le Chatelier)

Reaction shifts to the side with fewer moles of gas

Increase in volume (Le Chatelier)

Reaction shifts to the side with more moles of gas

Increase in reactant

Reaction creates more products (forward rxn)

Increase in product

Reaction creates more reactants (reverse rxn)

What happens to Keq if a reaction is reversed?

Keq is inverted

What happens to Keq if a reaction is multiplied by a factor?

Keq is raised to a power of the same factor

What happens to Keq if a reaction is divided by a factor?

Keq is the root of that factor

What happens to Keq if two or more reactions are added?

Multiply the corresponding Keq’s

Q > Keq

Reaction is reactant favored

Q < Keq

Reaction is product favored

Q = Keq

Neither direction is favored

Q = 0

The reaction does not proceed (only reactants)

Q = ∞

The reaction fully proceeds (only products)

Validating “x is small approximation“

x/initial concentration * 100

If x is less than or equal to 5% of the initial concentration

Then x is a small approximation and it can be ignored in the denominator

If x is greater than 5% of the initial concentration

Then x is not a small approximation, must be solved for by quadratic equation

Keq (Kc or Kp)

Values when the reaction is at equilibrium

Q

Value when the reaction is NOT at equilibrium, used to determine the direction of a reaction