Chemical Equilibria, Activity

Dynamic Equilibrium

concentrations of reactants and products remain constant and forward reaction rate equals reverse reaction rate (restaurant example)

Electrolyte

compound that dissociates into ions and is capable of conducting electricity when dissolved in solvent

Strong electrolyte examples

Ionic electrolytes (NaOH, NaCl, HCl)

Weak electrolyte examples

Covalent electrolyte (H2O, CH3COOH, NH3)

Non-electrolyte examples

Sugar, Alcohol, Oil

Acid

donates proton (Bronsted-Lowry) or accepts electrons (Lewis)

Base

accepts proton (Bronsted-Lowry) or donates electrons (Lewis)

Acid-Base Reaction/ Neutralization Reaction

Acid + base produces salt + water

Acid + base produces conjugate base + conjugate acid

Salt

ionic compound soluble or insoluble

Le Chatelier’s Principle

Equilibrium is disturbed by a change in the condition causing the equilibrium to shift to counteract the change.

What does Ksp represent?

The maximum ion concentration that can exist in a solution before precipitating

Common ion effect

application of Le Chatelier’s principle. Adding a compound with the same ion as product will shift the equilibrium to the left.

Factors that affect solubility

1. multiple and competing equilibria

   • decrease in pH increases solubility by increasing amount of compounds with basic anions, equilibrium shifts towards ions due to the newly created compounds dissolving increasing concentration of ions

   • weak conjugate bases are unaffected by change in pH (Cl-, HSO4-, NO3-, ClO4-, Br-, I-)

2. complex ion formation

   • increases solubility by adding ligand that forms stable complex with metal cations removing them from the solution, equilibrium shifts towards ions

Effective concentration of an ion

Ions are surrounded by other ions causing equilibrium to not only be affected by themselves

effective concentration is decreased by shielding it with other non-reactive ions representing the activity of the ion

inert salt decrease attraction between ion pairs increasing solubility

The Activity Coefficient (backwards y)

non-ideal behaviour of ions in solution caused by electrostatic interactions (attraction between ions)

[ x ] < 10^-4 M y is around 1

increasing concentration or adding more salt, there are more ions meaning stronger attractive forces (salting-in) y < 1

very high concentration cause ions to pull water more tightly and some water cannot act as solvent anymore (salting out). Compound prefers other compound ions not solvent causing precipitate to form y > 1

K’sp

Ksp does not change with ionic strength, K’sp is corrected for ionic strength

(decreased activity of ion will result in increase K’sp)

Ionic strength

measure of total electrolyte concentration

strong electrolytes with singly charged ions: ionic strength = molar concentration

multivalent ions: ionic strength > molar concentration

electrolyte effect depends only on ionic strength not types of ions: ionic strength <= 0.1 M

Debye-Huckel Equation

describes relationship between ion’s activity coefficient and ionic strength

decrease activity means less forces between ions, which increases the ionic strength