BUFFER SYSTEMS
What is the primary function of a buffer system?
To resist sudden changes in pH.
What type of reaction can proceed in both the forward and reverse directions?
A reversible reaction.
What condition exists when the forward and reverse reaction rates are equal?
Dynamic equilibrium.
Write the Kc expression for:
A+B⇌C+D
Kc=[C][D]/[A][B]
For A⇌B [A]=0.50M,[B]=2.0M. Find Kc
Kc=4.0
What two components commonly make up an acidic buffer?
A weak acid and its conjugate base.
What symbol represents a reversible reaction?
⇌
Why is chemical equilibrium called dynamic?
Because the forward and reverse reactions continue to occur.
Write the Kc expression for:
N2+3H2⇌2NH3
Kc=[NH3]2/[N2][H2]3
For: H2+I2⇌2HI : [H2]=0.20M,[I2]=0.20M,[HI]=1.20M , Find Kc
Kc= 36
When H+ is added to a buffer, which component reacts with it?
The conjugate base.
In a reversible reaction, what does the forward reaction produce?
Products from reactants.
What happens to the concentrations of reactants and products at equilibrium?
They remain constant.
What happens to the coefficients in a balanced equation when writing the Kc expression?
They become exponents.
For: A⇌B : if Kc=5.0 and [A]=0.40M, find [B].
[B] = 2.0M
When OH− is added to an acidic buffer, which component reacts with it?
The weak acid.
Give one example of a reversible process.
Evaporation and condensation of water.
Are the concentrations of reactants and products necessarily equal at equilibrium?
No
Which substances are generally omitted from a Kc expression?
Pure solids and pure liquids.
If Kc is much greater than 1, which side of the reaction is favored?
The product side.
Why can a buffer not maintain a constant pH indefinitely?
Its weak acid and conjugate base components can eventually be consumed.
Why can a reversible reaction eventually reach equilibrium?
Because the forward and reverse reactions continue until their rates become equal.
What is the difference between static and dynamic equilibrium?
Static equilibrium involves no continuing process, while dynamic equilibrium involves continuous forward and reverse reactions at equal rates.
CaCO3(s)⇌CaO(s)+CO2(g). write the equilibrium expression.
Kc=[CO2]
A reaction has Kc=0.002. What does this indicate?
The reactants are strongly favored.