15.5-15.7 Quiz

What equation do you use to calculate the equilibrium constant?

K_eq or K_c = ([C]^c[D]^d) / ([A]^a[B]^b) or K_P = (P_C^c * P_D^d) / (P_A^a * P_B^b)

How do you calculate Q?

= ([C]^c[D]^d) / ([A]^a[B]^b) or = (P_C^c * P_D^d) / (P_A^a * P_B^b); it is the reaction quotient; current/given concentrations NOT equilibrium concentrations

K = Q

at equilibrium; rates of forward and reverse reactions are equal and the concentrations remain constant over time

Q > K

reverse reaction must occur to reach equilibrium (produce reactants); products are consumed, reactants are formed, numerator in K_eq decreases and Q decreases until it equals K; favor reactants as system shifts left

Q < K

forward reaction must occur to reach equilibrium (produce products); favor products as system shifts right

Le Châtelier’s Principle

if a system at equilibrium is disturbed, the system will move in such a way as to counteract the disturbance; tries to reestablish equilibrium

Add concentration at equilibrium

equilibrium shifts away from increase; system reacts to consume more of substance it will shift away from the side that just gained more reactant or product to decrease that concentration; ex: If reactant is added, the forward reaction will be favored to decrease reactants and increase product concentration until a new equilibrium is reached.

Removing concentration at equilibrium

equilibrium shifts toward decrease; system reacts to produce more of substance; it will shift toward the side where the reactant or product was just removed to increase that product; ex: If a reactant is removed, the reverse reaction will be favored to increase reactant concentration and decrease product concentration.

Decrease Volume at equilibrium

will increase pressure; equilibrium shifts in direction with fewer moles of gas; remove gases and decrease pressure; IF EQUAL MOLES OF GAS, no effect

Increase Volume at Equilibrium

will decrease pressure; equilibrium shifts in direction with more moles of gas; add gases and increase pressure; IF EQUAL MOLES OF GAS, no effect

Increase Pressure at equilibrium

shifts in direction with fewer moles

Decrease pressure at equilibrium

shifts in direction with more moles of gas

ΔH > 0 meaning

endothermic; heat is a reactant; forward direction is favorable; adding heat favors away from increase

ΔH < 0 meaning

exothermic; heat is a product; reverse reaction is favorable

increasing temperature in endothermic reaction

reaction shifts right (toward products)

decreasing temperature in endothermic reaction

reaction shifts left (toward reactants)

increasing temperature in exothermic reaction

reaction shifts left toward reactants

decreasing temperature in exothermic reaction

reaction shifts right toward products

With temperature, the equilibrium shifts in the direction that consumes the _______

excess reagent; heat

Effect of a catalyst on an equilibrium

no effect; will only speed up the reaction rate

What will happen if insert substances are added?

does not affect the equilibrium