The study of Chemical reactions, using the tools of Statistical physics, in particular Thermodynamics

Chemical energetics

Reaction thermodynamics

Uses the theory of Statistical mechanics of multispecies systems

Balance of Chemical potentials of reactants and products (note that Chemical potential is proportional to Gibbs free energy in the Grand canonical ensemble). See video.

The chemical potential energy difference can be epxpressed as:

$\Delta G = \Delta G^0' + RT \ln{\frac{[A]}{[B]}}$

where $\Delta G^0'$ is the change in Gibbs free energy of a reaction of the form $A \rightarrow B$, $[i]$ represents the concetration of the Chemical species $i$.

As can be derived from the Second law of thermodynamics, at constant pressure and temperature, an spontaneous process occurs if its Gibbs free energy change is negative.

See note in tablet

Chemical equilibrium and the effects of pressure and temperature

Energy is absorbed to break bonds and released when bonds are made. Energy changes in a reaction are calculated by bond energies and shown by energy diagrams. See here

Chemical kinetics

Non-equilibrium statistical physics of chemical reactions, in particular the rates at which they occur.