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What is Physical Chemistry?

What is Physical Chemistry?

Physical chemistry is a branch of chemistry that studies the principles from physics underlying chemical reactions. It provides deep insights into the behaviors of molecules, the forces they experience, and their interactions and chemical reactions.The term "physical chemistry" was introduced by Mikhail Lomonosov in 1752. Since then, it has seen significant contributions from notable scientists such as Josiah Willard Gibbs, Wilhelm Ostwald, Jacobus Henricus van't Hoff, and Linus Pauling.Key...

Chemical Reactions

Chemical Reactions

A chemical reaction is a process by which the bonds in the atoms of substances are rearranged to generate new substances. Matter cannot be created or destroyed in a chemical reaction—the same type and number of atoms that make up the reactants are still present in the products. Merely, the rearrangement of chemical bonds produces new compounds.
Chemical Reactions Rearrange Atoms into New Substances
A chemical reaction takes starting materials—the reactants—and changes them into different...

Chemical Reactions

Chemical Reactions

A balanced chemical equation provides the information of chemical formulas of the reactants and products involved in the chemical change. A reaction’s stoichiometry helps predict how much of the reactant is needed to produce the desired amount of product, or in some cases, how much product will be formed from a specific amount of the reactant.
The relative amounts of reactants and products represented in a balanced chemical equation are often referred to as stoichiometric amounts. However, in...

The Small x Assumption

The Small x Assumption

If a reaction has a small equilibrium constant, the equilibrium position favors the reactants. In such reactions, a negligible change in concentration may occur if the initial concentrations of reactants are high and the Kc value is small. In such circumstances, the equilibrium concentration is approximately equal to its initial concentration. This estimation can be used to simplify the equilibrium calculations by assuming that some equilibrium concentrations are equal to the initial...

Introduction to Chemical Reactions

Introduction to Chemical Reactions

All chemical reactions begin with a reactant, the general term for one or more substances entering the reaction. Sodium and chloride ions, for example, are the reactants in the production of table salt. One or more substances produced by a chemical reaction are called the product. Chemical reactions follow the law of conservation of mass, which means that matter cannot be created nor destroyed in a chemical reaction. The components of the reactants—the number of atoms and the elements—are all...

Thermodynamics: Chemical Potential and Activity

Thermodynamics: Chemical Potential and Activity

The effective concentration of a species in a solution can be expressed precisely in terms of its activity. Activity considers the effect of electrolytes present in the vicinity of the species of interest and depends on the ionic strength of the solution. The activity of a species is expressed as the product of molar concentration and the activity coefficient of the species.
The thermodynamic equilibrium constant is more accurately defined in terms of activity rather than concentration.

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Related Experiment Video

Updated: Jun 13, 2026

Analyzing Melts and Fluids from Ab Initio Molecular Dynamics Simulations with the UMD Package

Analyzing Melts and Fluids from Ab Initio Molecular Dynamics Simulations with the UMD Package

Published on: September 17, 2021

Adventures in physical chemistry.

Harden McConnell¹

¹Department of Chemistry, Stanford University, Stanford, California 94305, USA. harden@stanford.edu

Annual Review of Biophysics

|May 14, 2010

Summary

This research developed theoretical equations for free radicals and NMR spectra. It provided early evidence for cell membrane fluidity using spin labels and discovered phase separations in membranes.

Area of Science:

Chemical Physics
Biophysics
Immunology

Background:

Developed theoretical equations for nuclear hyperfine splittings in free radicals and NMR spectra for chemical reaction rates.
Utilized paramagnetic probes (spin labels) to investigate cell membrane properties.

Discussion:

Provided early evidence for the liquid-like behavior of cell membranes.
Measured lateral and transverse diffusion of phospholipids in bilayer membranes using spin labels.
Discovered liquid-liquid phase separations in monolayer membranes containing phospholipids and cholesterol.

Key Insights:

Established theoretical frameworks for analyzing electron spin distributions and reaction kinetics.
Demonstrated the utility of spin labels in elucidating membrane dynamics and phase behavior.

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Last Updated: Jun 13, 2026

Analyzing Melts and Fluids from Ab Initio Molecular Dynamics Simulations with the UMD Package

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Showed that antigenic peptides bind to class II MHC molecules, activating T-helper cells.

Outlook:

Further exploration of membrane biophysics and phase behavior.
Application of developed equations in advanced spectroscopy and chemical kinetics.
Investigating the role of membrane composition in immune response activation.