Entropy ($S$): Measure of disorder or energy dispersal

• Units: J/mol - K
• Standard entropy ($S degrees$): Entropy at standard conditions (1 bar, 25 degrees C)

$\Delta S$ positive when:

• Solid -> liquid -> gas
• More moles of gas produced
• Dissolving (usually)
• Mixing
• Temperature increase

$\Delta S degrees _{rxn} = \sum S degrees _{products} - \sum S degrees _{reactants}$

Phase changes:

• Fusion ($\Delta S_{fus} > 0$)
• Vaporization ($\Delta S_{vap} > 0$, much larger than $\Delta S_{fus}$)

Spontaneous: Occurs without outside intervention

• Determined by enthalpy ($\Delta H$) and entropy ($\Delta S$) effects

Process spontaneous if:

• Releases energy (exothermic, $\Delta H < 0$), OR
• Increases disorder ($\Delta S > 0$), OR
• Both

At high temperature: entropy effects dominate At low temperature: enthalpy effects dominate

$\Delta G = \Delta H - T\Delta S$

• $\Delta G < 0$: Spontaneous (thermodynamically favored)
• $\Delta G = 0$: System at equilibrium
• $\Delta G > 0$: Non-spontaneous (thermodynamically disfavored)

$\Delta G degrees = -RT\ln K$

• $\Delta G degrees < 0$: $K > 1$ (products favored)
• $\Delta G degrees = 0$: $K = 1$
• $\Delta G degrees > 0$: $K < 1$ (reactants favored)

Non-standard conditions: $\Delta G = \Delta G degrees + RT\ln Q$

Anode: Oxidation occurs; electrons leave; negative electrode in galvanic cell Cathode: Reduction occurs; electrons enter; positive electrode in galvanic cell Salt bridge: Maintains electrical neutrality; allows ion flow

$E degrees _{cell} = E degrees _{cathode} - E degrees _{anode}$

Spontaneous: $E degrees _{cell} > 0$

Electrolytic cell: Uses electrical energy to drive non-spontaneous redox reaction

• Anode: Still oxidation (but positive electrode)
• Cathode: Still reduction (but negative electrode)
• External voltage source required

$m = \frac{Q \times M}{n \times F} = \frac{I \times t \times M}{n \times F}$

• m = mass (g)
• Q = charge (Coulombs)
• I = current (Amps)
• t = time (s)
• M = molar mass (g/mol)
• n = moles of electrons transferred
• F = 96,485 C/mol e- (Faraday's constant)