Chemistry Chapter 5 & 6: Equilibrium & Acid-Base Equilibrium

Reaction Quotient, Q

helps determine the direction a system will shift to reach equilibrium when all the initial concentrations are nonzero

Relationship between the values of Q & K

indicative of each other, the same

Q=K

system is at equilibrium, and no shift will occur

Q>K

system shifts to the left, consumes products, and forms reactants until equilibrium is achieved; the reverse reaction takes over

Q<K

system shifts to the right, consumes reactants, and forms products to attain equilibrium; the forward reaction takes over

In what instances can you make assumptions?

In certain instances we can assume the x term (i.e. the change) is small enough to be negligible: K for the equilibrium is 10^-3 or smaller

LeChatelier’s Principle

if a change is imposed on a system at equilibrium, the position of the equilibrium will shift in a direction that tends to reduce that change ( concentration, pressure and temperature)

Changes in reactant and/or product concentrations

system shifts in the direction that compensates for the imposed change

Changes in equilibrium pressure

Three ways to change the pressure: add or remove a gaseous reactant or product, add an inert gas (noble gas; one not involved in the reaction) or change the volume of the container

If volume is reduced…

pressure will increase and the system will shift to the right (forward reaction) in response

Changes in equilibrium temperature

value of K changes with temperature; proportionate

Exothermic reaction

shift will be in the direction that consumes energy (to the left)

Endothermic reaction

increase in temperature will cause the equilibrium to shift to the right and the value of K to increase

Arrhenius acid

any substance that will increase the concentration of H+ ions when dissolved in water

Arrhenius base

any substance that will increase the concentration of OH- ion when dissolved in water

Neutralization Reaction

Acid + Base —> Salt + Water

Bronsted-Lowry Acid

proton (H+) donor; must have a transferable proton

Bronsted-Lowry Base

proton (H+) acceptor; must have a lone pair

Conjugate acid

H+ donor; what is generated when the base accepts a proton

Conjugate base

H+ acceptor; what is left after the acid donates its proton