Chem/Phys Deck 5: Equilibrium, Solubility, Acids/Bases & Solutions

What is chemical equilibrium?

A dynamic state where the forward and reverse reaction rates are equal.

Reactants and products are still reacting, but there's no net change.

At equilibrium, do reactant and product concentrations have to be equal?

No.

Only the rates are equal.

What is the equilibrium constant (K)?

A ratio of products to reactants at equilibrium.

Large K → products favored.

Small K → reactants favored.

If K > 1, what is favored?

Products.

If K < 1?

Reactants.

What happens if more reactant is added?

The equilibrium shifts right to consume it.

What happens if more product is added?

The equilibrium shifts left

What happens if a product is removed?

The equilibrium shifts right to replace it.

What happens if a reactant is removed?

Back:
The equilibrium shifts left.

Does a catalyst change the equilibrium position?

No.

It only helps the system reach equilibrium faster.

What does Ksp represent?

The solubility product constant.

It measures how much an ionic compound dissolves.

If Q > Ksp, what happens?

A precipitate forms.

If Q < Ksp?

More solid can dissolve

If Q = Ksp?

The solution is saturated and at equilibrium.

What is the common ion effect?

Adding an ion already present in solution decreases solubility

Why does adding NaCl decrease AgCl solubility?

Extra Cl⁻ shifts the dissolution equilibrium left

Are nitrates (NO₃⁻) generally soluble?

Yes. Always assume nitrates are soluble.

Are alkali metal salts soluble?

Yes.

Group 1 ions are essentially always soluble.

Are ammonium (NH₄⁺) salts soluble?

Yes.

What's the difference between a strong and weak acid?

Strong acids completely dissociate.

Weak acids only partially dissociate.

Does a strong acid always have a low pH?

Not necessarily.

Concentration matters too.

What is a strong base?

A base that completely dissociates in water.

Examples:

• NaOH

  • KOH

What is a buffer?

A solution that resists changes in pH.

Usually made of:

• weak acid + conjugate base
  OR

• weak base + conjugate acid

How does a buffer resist added acid?

The conjugate base accepts H⁺.

How does a buffer resist added base?

The weak acid donates H⁺

What is the Henderson-Hasselbalch equation?

pH=pKa​+log(A−/HA​)

If [A⁻] = [HA], what is true?

pH = pKa

At the equivalence point of a strong acid–strong base titration, what is the pH?

Approximately 7.

before the equivalence point, what is in excess?

The analyte (the solution originally in the flask

After the equivalence point?

The titrant is in excess

What is molarity?

M=moles/Liters

What equation is used for dilution?

M1​V1​=M2​V2​

During dilution, what stays constant?

The number of moles of solute

Does increasing pressure affect every equilibrium?

No.

Only equilibria involving gases

If a pure solid is added to a heterogeneous equilibrium, does K change?

No.

Pure solids and pure liquids are not included in the equilibrium expression

Are catalysts included in the equilibrium constant?

No.