Physical Chemistry Cheat Sheet

The core ideas of Physical Chemistry distilled into a single, scannable reference — perfect for review or quick lookup.

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Quick Reference

Thermodynamics

The study of energy transformations in chemical systems, governed by three fundamental laws that describe energy conservation, entropy increase, and the absolute zero of temperature. Thermodynamics determines whether a reaction is spontaneous through the Gibbs free energy.

Chemical Kinetics

The study of reaction rates, including how fast reactions occur and the step-by-step pathways (mechanisms) by which reactants transform into products. Rate laws express the mathematical relationship between concentration and reaction speed.

Quantum Chemistry

The application of quantum mechanics to chemical systems, explaining electronic structure, chemical bonding, and molecular properties by solving the Schr\u00f6dinger equation for atoms and molecules.

Gibbs Free Energy

A thermodynamic potential ($G = H - TS$) that combines enthalpy and entropy to predict whether a process will occur spontaneously at constant temperature and pressure. A negative change in $G$ indicates a spontaneous process.

Activation Energy

The minimum energy ($E_a$) that reactant molecules must possess for a chemical reaction to occur. It represents the energy barrier between reactants and products on a potential energy surface.

Entropy

A thermodynamic quantity ($S$) that measures the dispersal of energy and the number of accessible microstates in a system. The Second Law of Thermodynamics states that the total entropy of an isolated system always increases.

Phase Equilibrium

The condition where two or more phases of a substance coexist in thermodynamic equilibrium, with no net transfer of matter between phases. Phase diagrams map the conditions of temperature and pressure at which phases are stable.

Chemical Equilibrium

The state in which the rates of the forward and reverse reactions are equal, so the concentrations of reactants and products remain constant over time. The equilibrium constant $K$ quantifies the ratio of product to reactant concentrations.

Spectroscopy

The study of how matter interacts with electromagnetic radiation. Different types of spectroscopy (UV-Vis, IR, NMR, mass spectrometry) probe different molecular properties such as electronic transitions, molecular vibrations, and nuclear environments.

Electrochemistry

The study of chemical reactions that involve the transfer of electrons, particularly those occurring at electrode-solution interfaces. It encompasses both galvanic cells (which produce electricity) and electrolytic cells (which use electricity to drive reactions).

Key Terms at a Glance

Activation Energy:The minimum energy required for a chemical reaction to proceed, representing the energy barrier on the reaction coordinate.

Adiabatic Process:A thermodynamic process in which no heat is exchanged between the system and its surroundings ($q = 0$).

Boltzmann Constant:A fundamental physical constant ($k_B = 1.381 \times 10^{-23}$ J/K) that relates the average kinetic energy of particles in a gas to the temperature.

Catalyst:A substance that increases the rate of a chemical reaction by lowering the activation energy without being consumed in the process.

Chemical Potential:The partial molar Gibbs free energy of a component in a mixture; it describes how the free energy changes when the amount of that component changes.

Colligative Properties:Properties of solutions that depend on the ratio of solute to solvent particles, not on the identity of the solute.

Electrochemical Cell:A device that converts chemical energy into electrical energy (galvanic cell) or uses electrical energy to drive a non-spontaneous reaction (electrolytic cell).

Endothermic:A process that absorbs heat from the surroundings, characterized by a positive enthalpy change ($\Delta H > 0$).

Enthalpy:A thermodynamic state function defined as $H = U + PV$, representing the total heat content of a system at constant pressure.

Entropy:A thermodynamic quantity measuring the degree of energy dispersal or the number of accessible microstates in a system.

Equilibrium Constant:A dimensionless quantity ($K$) expressing the ratio of product to reactant activities at chemical equilibrium for a given reaction at a specific temperature.

Exothermic:A process that releases heat to the surroundings, characterized by a negative enthalpy change ($\Delta H < 0$).

Fugacity:An effective pressure that replaces the true pressure in thermodynamic equations for real gases, accounting for deviations from ideal behavior.

Gibbs Free Energy:A thermodynamic potential ($G = H - TS$) used to predict the spontaneity of a process at constant temperature and pressure.

Half-Life:The time required for the concentration of a reactant to decrease to half its initial value, commonly used in first-order kinetics where $t_{1/2} = \frac{\ln 2}{k}$.

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