Essential Chemistry Principles & Formulas

Fundamental Chemistry Concepts

Gas Laws

• Boyle's Law: At constant temperature (T), volume (V) is inversely proportional to pressure (P).
• Gay-Lussac's Law: At constant pressure (P), volume (V) is directly proportional to temperature (T).

Atomic Structure & Periodic Trends

• Quantum Numbers: Describe atomic orbitals: n (principal), l (azimuthal, 0, 1, 2...), m (magnetic, ±l), and s (spin).
• Periodic Table Elements: Transition elements are found in the center of the periodic table. Representative elements are in Groups 1, 2, and 13-18.
• Atomic Radius: ab-IZK

Chemical Bonding & Properties

• Ionic Compounds:
  • No discrete molecules; forces are electrostatic.
  • Upper-middle melting and boiling points.
  • Hard but brittle.
  • Electrical insulators in solid form; conduct current when fused.
  • Dissolve in highly polar liquids.
• Metals:
  • Tend to eject electrons.
  • Characteristic brightness.
  • Excellent conductors of electricity and heat.
  • Exhibit large, medium, or low mechanical hardness.
  • High melting points; generally do not dissolve.
• Covalent Bonds (Covalent Crystals):
  • No free electrons.
  • Very high melting points.
  • Very stiff solids.
  • Good electrical insulators, poor conductors of heat.
  • Insoluble.

Molecular Geometry (VSEPR Theory)

• AB2: (e.g., BeCl2) - Linear
• AB3: (e.g., BF3) - Trigonal Planar
• AB4: (e.g., CH4) - Tetrahedral
• AB5: (e.g., PCl5) - Trigonal Bipyramidal
• AB6: (e.g., SF6) - Octahedral

Chemical Calculations & Thermodynamics

Concentration Units

• Volume Percent (% v/v): (V_solute / V_solution) × 100%
• Mass Percent (% m/m): (mass_solute / mass_solution) × 100%
• Molarity (M): n_solute / V_solution (L)
• Mole Fraction (X): n_solute / (n_solute + n_solvent)

Thermodynamics Basics

• Work (W): W = -P∆V
• Heat (q): q = mc∆T
• Enthalpy (H): H = U + PV
  • At constant volume (V): q_v = ∆U
  • Internal Energy Change: ∆U = q - P∆V
  • At constant pressure (P): q_p = ∆H

Reaction Energy & Enthalpy

• Reaction Internal Energy (∆U_r): U_products - U_reactants
• Reaction Enthalpy (∆H_r): H_products - H_reactants
  • Positive ∆H_r: Endothermic reaction.
  • Negative ∆H_r: Exothermic reaction.

Gibbs Free Energy & Spontaneity

• Gibbs Free Energy Change (∆G): ∆G = ∆H - T∆S
• Reaction Gibbs Free Energy (∆G_r): G_products - G_reactants
• Reaction Entropy (∆S_r): S_products - S_reactants
• Spontaneity Conditions:
  • If ∆H < 0 and ∆S > 0: Spontaneous at all temperatures (∆G < 0).
  • If ∆H < 0 and ∆S < 0: Spontaneous at low temperatures (∆G < 0).
  • If ∆H > 0 and ∆S > 0: Spontaneous at high temperatures (∆G < 0).
  • If ∆H > 0 and ∆S < 0: Non-spontaneous at any temperature (∆G > 0).

Chemical Equilibrium

• Equilibrium Constant (K_c): K_c = [Products] / [Reactants] (concentrations in mol/L)
• Pressure Equilibrium Constant (K_p): K_p = K_c (RT)^∆n (where ∆n is the change in moles of gas)
• Molarity & Moles: Molarity (M) = moles (n) / volume (V in liters); thus, n = M × V.

pH Calculations

• pH: pH = -log[H⁺]

Reaction Kinetics & Acid-Base Chemistry

Reaction Rates & Orders

• Determine reaction orders from experimental data.
• Rate Law: v = k[A]^α[B]^β
• Comparing Rates: v₂ / v₁ = ([A]₂^α) / ([A]₁^α)
• Rate Constant (k): k = v / ([A]^α[B]^β)

Arrhenius Equation & Activation Energy

• Arrhenius Equation: k = Ae^-Ea/RT
• Activation Energy (Ea): The minimum energy required for a reaction to occur.

Strong Acids and Bases

• Strong Acids: HClO₄, HI, HBr, HCl, H₂SO₄, HNO₃
• Strong Bases: Hydroxides of Group 1 and some Group 2 metals (e.g., NaOH, KOH, Ca(OH)₂). (Note: Conjugate bases of strong acids are generally weak bases.)

Catalysts and Inhibitors

• Catalysts:
  • Substances that alter (usually increase) reaction rates.
  • Recovered chemically unchanged at the end of the process.
  • Often highly specific.
  • Do not alter thermodynamic variables.
• Inhibitors:
  • Substances that, in small amounts, decrease reaction rates.
  • Are not consumed or altered in the reaction.

Stoichiometry & Ideal Gas Law Applications

Concentration & Molar Mass Calculations

• Mass Percent (% m/m): (mass_solute / mass_solution) × 100%
• Mole Fraction (X): n_solute / (n_solute + n_solvent)
• Partial Pressure (P_i): P_i = n_i RT / V (from Ideal Gas Law)
• Molar Mass (M) from Density: M = dRT / P
• Molarity (M): M = n_solute / V_solution (L)