BUFFER SYSTEMS
What does a buffer resist?
Sudden changes in pH.
What does the symbol ⇌\rightleftharpoons⇌ indicate?
A reversible reaction.
What is the defining condition of dynamic equilibrium?
The forward and reverse reaction rates are equal.
For: 2A⇌B, write the Kc expression.
Kc=[B]/[A]2
What happens when more reactant is added to an equilibrium system?
The system shifts toward the products.
In the reaction: HA⇌H++A− which species reacts with added H+?
A−, the conjugate base.
What is the reverse reaction?
The reaction that converts products back into reactants.
Does a reaction stop when equilibrium is reached?
No
For: 2SO2+O2⇌2SO3, write the Kc expression.
Kc=[SO3]2/[SO2]2[O2]
What happens when a product is removed?
The system shifts toward the products.
Which component of a buffer reacts with added OH-?
The weak acid.
Can a reversible reaction occur in both directions at the same time?
Yes.
What remains constant at equilibrium?
The concentrations of reactants and products.
If Kc=100, which side is favored?
The product side.
For an endothermic reaction, what happens when temperature increases?
The equilibrium shifts toward the products.
What happens to the pH of a buffer when a small amount of acid is added?
The pH changes only slightly.
What happens to the forward and reverse reaction rates as equilibrium is approached?
They become closer until they are equal.
What kind of system is generally needed to establish chemical equilibrium?
A closed system.
If Kc=0.0005 which side is favored?
The reactant side.
For an exothermic reaction, what happens when temperature increases?
The equilibrium shifts toward the reactants.
Why does a buffer resist pH changes?
Its components react with added H+ or OH−
Why does a reversible reaction not necessarily convert all reactants into products?
The reverse reaction also occurs and may eventually balance the forward reaction.
Explain why equilibrium does not mean that the amounts of reactants and products are equal.
Equilibrium means equal reaction rates, not necessarily equal concentrations.
Why are pure solids and pure liquids omitted from equilibrium expressions?
Their concentrations remain essentially constant.
For:N2(g)+3H2(g)⇌2NH3(g), what happens when pressure increases?
The equilibrium shifts toward NH3, the side with fewer gas particles.