2.1 QUALITATIVE CHEMISTRY

Kinetics

speed or rate of reaction

Reaction rate

change in the concentration (M) of a reactant or a product with time (s) (expressed as M/s)

Collision Theory of Chemical Kinetics

• Activation energy (E_a)

minimum amount of energy required to initiate a chemical reaction

 FACTORS AFFECTING REACTION RATE

• Nature of reactants & its state of subdivision 

• Concentration:

• Temperature

Concentration

• Rate ɑ= no. of collisions / s 

Temperature

the faster the molecule moves ↑KE

Arrhenius equation

temperature dependence rate constant 

Catalyst

increases the rate of a chemical reaction without itself being consumed 

CHEMICAL EQUILIBRIUM IS ACHIEVED WHEN

• Rates of the forward and reverse reactions are equal and the concentrations of the reactants and products remain constant

• rf = rr concentration constant

Equilibrium Constant 

aA+bB → cC+dD

Homogenous Equilibrium

All the reacting species are in the same phase

Heterogenous Equilibrium

The reacting species are in two or more phases

Equilibrium Constant (Kc) helps to:

Predict the direction of a reaction

Reaction quotient (Qc)

calculated by substituting the initial concentrations of the reactants and products into the equilibrium constant (Kc) expression.

Qc>Kc

system proceeds from right to left to reach equilibrium

Qc= Kc

system is at equilibrium

Qc<Kc

system proceeds from left to right to reach equilibrium

Le Châtelier's Principle

• If an external stress is applied to a system at equilibrium, the system adjusts in such a way that the stress is partially offset as the system reaches a new equilibrium position

 FACTORS AFFECTING CHEMICAL EQUILIBRIUM

• concentration

• pressure and volume

• temperature

Concentration:

• Backward reaction favored

⬆Product concentration

↓ reactant concentration

Concentration:

• Forward reaction favored

↓ Product concentration

⬆Reactant concentration

Pressure & Volume

↑ Pressure / ↓  Volume

Favors fewest moles of gas

Pressure & Volume

↓ Pressure / ↑ Volume

Favors greater moles of gas

Temperature

• Exothermic

↑ Temperature favors backward (reactants)

↓ Temperature favors forward (products)

Temperature

• Endothermic

↑ Temperature favors forward (products)

↓ Temperature favors backward (reactants)

Adding a Catalyst

• does not change K

• no shift in the position of an equilibrium system only change in temperature will affect EQUILIBRIUM CONSTANT

ARRHENIUS

Acid -substance that produces H+ (H3O+) in water

Base -substance that produces OH- in water

BRONSTED

Acid - Proton donor

Base - Proton acceptor

LEWIS

Acid - Electron acceptor

Base - Electron donor

STRONG ELECTROLYTES

• strong acids, strong bases & salts containing the ions of strong acids & bases

• 100% ionization / dissociation in H₂O

• undergoes irreversible reaction

Strong Acid

• HCI

• HBr

• HI

• H₂SO₄

• HClO₄

• HNO₃

Strong Base

• NaOH

• KOH

• Ba(OH)₂

• Sr(OH)₂

• Ca(OH)₂

• Mg(OH)₂

Weak Acids (HA)

• Not completely ionized / dissociated 

• Undergoes reversible reaction

Amphoteric

May act as acid or base

Autoionization of Water

H2O (l) ⇌ H+ (aq) + OH- (aq)

Ion-Product Constant (Kw)

pH Formula

pOH Formula

pKw Relationship

pH & Concentration Trend

↑pH [H+]↓

Isohydric Solution

A solution with the same pH as another solution to which it is compared

Weak Acids (HA) and Acid Ionization Constants

HA (aq) ⇌ H⁺ (aq) + A⁻ (aq)

Ka (Acid ionization constant)

Weak Bases and Base Ionization Constants

NH₃ (aq) + H₂O (l) ⇌ NH₄⁺ (aq) + OH⁻ (aq)

Kb (Base ionization constant)

SALTS

• Compounds made up of the cation of the base and the anion of the acid

• Compounds made up of the metal & non-metal 

• Weaker ions will undergo hydrolysis

Neutral Solutions

• ion of strong base + ion of strong acid

• no hydrolysis

Basic Solutions

• ion of strong base + ion of weak acid

• will hydrolyze

Acid Solutions

• ion of strong acid + ion of weak base

• will hydrolyze

ion of strong acid + ion of weak base lowly charged

ion of strong acid + ion of weak base highly charged

Solutions in which both the cation and the anion hydrolyze

• Kb for anion > Ka for cation

solution will be basic

Solutions in which both the cation and the anion hydrolyze

Kb for anion < Ka for cation

 solution will be acidic

Solutions in which both the cation and the anion hydrolyze

Kb for anion ≈ Ka for cation

solution will be neutral only for NH₄CH₃COO

Metallic oxide/basic oxide/basic anhydride + water

base

Non-metallic oxide/acid oxide/acid anhydride +water

acid

Amphoteric oxide

can be base or acid

BUFFER SOLUTION

• Solution of: 

  • weak acid + its salt

  • weak base + its salt

Buffers

Have the ability to resist changes in pH upon the addition of small amounts of either acid or base

Buffer capacity

Amount of acid or base the buffer can neutralize before the pH begins to change in an appreciable degree

Henderson Hasselbalch equation

SOLUBILITY PRODUCT CONSTANT (K_sp)

Ca₃(PO₄)₂ (s) ⇌ 3 Ca₂+ (aq) + 2 PO₄^3- (aq) 

Ksp = [Ca²⁺]³ [PO₄^3-]² 

• ↑ Ksp ↑ soluble 

• ↓ Ksp ↓ soluble

Q < Ksp

Unsaturated solution

No precipitate

Q = Ksp

Saturated solution

No precipitate

Q > Ksp

Super saturated solution

Precipitation

FRACTIONAL PRECIPITATION

• Removing selected ions from solution while leaving others with similar properties in solution 

Complex ion

Ion containing a central metal carbon bonded to one/ more molecules or ions (LIGANDS)

Formation constant / Stability constant (K_f)

Equilibrium constant for the complex ion