Chem 1412: Key Concepts in Thermodynamics and Reactions

First Law of Thermodynamics

Energy cannot be created or destroyed; only transferred.

Internal Energy (ΔE)

ΔE = q + w (heat + work)

Enthalpy (ΔH)

Heat content of a system at constant pressure.

Endothermic

Absorbs heat (ΔH > 0)

Exothermic

Releases heat (ΔH < 0)

Hess's Law

Add enthalpy changes of steps to get overall ΔH.

Calorimetry

q = mcΔT (used to measure heat changes)

Entropy (ΔS)

Measure of disorder; increases in spontaneous processes.

Gibbs Free Energy (ΔG)

ΔG = ΔH - TΔS

Spontaneous Process

ΔG < 0: spontaneous

Nonspontaneous Process

ΔG > 0: nonspontaneous

Standard Gibbs Free Energy

Related to equilibrium constant: ΔG° = -RTlnK

Reaction Rates

How fast reactants become products.

Rate Law

Rate = k[A]^m[B]^n

Rate Constant (k)

Depends on temperature, not concentration.

Integrated Rate Laws

Used to determine concentration over time.

Half-life (t½)

First-order: t½ = 0.693/k

Catalysts

Lower activation energy without being consumed.

Equilibrium Constant (K)

K > 1: products favored; K < 1: reactants favored.

Le Chatelier's Principle

System adjusts to relieve stress (change in concentration, temp, pressure).

Q vs. K

Q < K: shift right; Q > K: shift left.

Arrhenius Definition of Acids and Bases

Acids donate H⁺, bases donate OH⁻.

Bronsted-Lowry Definition of Acids and Bases

Acids donate protons; bases accept protons.

Strong vs. Weak Acids/Bases

Strong ones dissociate completely.

pH and pOH

pH = -log[H⁺]; pOH = -log[OH⁻]; pH + pOH = 14.

Ka and Kb

Acid/base dissociation constants.

Buffer Solutions

Resist pH change (made of weak acid + conjugate base).

Henderson-Hasselbalch Equation

pH = pKa + log([A⁻]/[HA])

Ksp (Solubility Product)

Equilibrium constant for dissolving salts.

Common Ion Effect

Adding a common ion decreases solubility.

Precipitation

Compare Q to Ksp.

Complex Ions

Metal ion + ligand; increases solubility of metal salts.

Redox Reactions

Oxidation (loss of e⁻), Reduction (gain of e⁻).

Galvanic (Voltaic) Cells

Spontaneous redox reactions produce electricity.

Anode

Site of oxidation.

Cathode

Site of reduction.

Electrons Flow Direction

Electrons flow anode → cathode.

Cell Notation

Zn(s) | Zn²⁺ || Cu²⁺ | Cu(s)

Standard Cell Potential (E°cell)

E°cell = E°cathode - E°anode.

Nernst Equation

E = E° - (0.0591/n) logQ.

Types of Decay

Alpha (α): loses ⁴₂He; Beta (β⁻): neutron → proton + electron; Positron (β⁺): proton → neutron + positron; Gamma (γ): high energy radiation.

Half-Life Calculations

N = N₀(½)^(t/t½).

Fission

Splitting heavy nucleus (used in nuclear reactors).

Fusion

Combining light nuclei (sun's energy).

Coordination Number

Number of ligand bonds.

Nomenclature in Coordination Chemistry

Follows IUPAC rules (e.g., [Cr(NH₃)₆]³⁺ is hexaamminechromium(III) ion).

Isomerism

Structural: different connectivity; Geometric (cis/trans), Optical (mirror images).