Chemical Thermodynamics Cheatsheet

Cheat Codes & Shortcuts

• System: Part of universe under study.
• Surroundings: Everything else outside the system.
• First Law: Energy cannot be created or destroyed, only transformed.
• Internal Energy (\( \Delta U \)): Total energy (kinetic + potential) of system.
• Enthalpy (\( H \)): \( H = U + PV \), heat change at constant pressure.
• Entropy (\( S \)): Measure of disorder or randomness.
• Gibbs Free Energy (\( G \)): \( G = H - TS \), spontaneity criterion.
• Spontaneity: \( \Delta G < 0 \) (spontaneous), \( \Delta G > 0 \) (non-spontaneous).
• Second Law: Entropy of universe increases for spontaneous processes.
• Standard Conditions: 1 atm, 298K, 1M concentration.

Quick Reference Table

Term	Formula / Definition	Notes / Example
First Law	\( \Delta U = q + w \)	q = heat, w = work
Enthalpy	\( \Delta H = \Delta U + P \Delta V \)	Exothermic: \( \Delta H < 0 \), Endothermic: \( \Delta H > 0 \)
Entropy	\( \Delta S = S_{final} - S_{initial} \)	Greater randomness → higher S
Gibbs Free Energy	\( \Delta G = \Delta H - T \Delta S \)	\( \Delta G < 0 \) means spontaneous
Second Law	Entropy increases in spontaneous processes	Melting, mixing, diffusion
Standard State	1 atm, 298K, 1M	Used in thermochemical data

Advice

Thermodynamics Quick Tips

• First Law: Energy is conserved; calculate \( \Delta U \) with sign convention.
• Gibbs equation: \( \Delta G \) at 298K shows spontaneity.
• Entropy trend: Solids < Liquids < Gases for S value.
• Standard enthalpy change: \( \Delta H^\circ \) at 1 atm and 298K.
• Spontaneity: If \( \Delta G < 0 \), process occurs naturally.

Thermodynamics Speed Quiz

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