What is physical chemistry?
Physical chemistry asks how and why chemical change happens, rather than simply what reacts with what. It applies the tools of physics and mathematics to chemical systems in order to explain energy flow, reaction speed, and the position a reaction settles into.
It is the branch that answers the awkward questions. Why does a reaction release heat? Why does it stop before all the reactants are used up? Why does raising the temperature speed it up so dramatically? Each answer comes from a quantitative model rather than a rule of thumb.
Its main areas
- Thermodynamics: energy, enthalpy, entropy and free energy, and what makes a change spontaneous
- Kinetics: reaction rates, rate laws, activation energy and catalysis
- Equilibrium: reversible reactions, the equilibrium constant and Le Chatelier's principle
- Electrochemistry: redox reactions, cells, electrode potentials and electrolysis
- Quantum chemistry and spectroscopy: how electrons occupy orbitals and how molecules interact with light
The maths, in context
Physical chemistry carries more equations than other branches, but each one encodes a physical idea. Understanding what the symbols mean makes the algebra follow, which is why the definitions below explain the concept before the formula.