Reaction dynamics is a field within physical chemistry

Physical chemistry

Physical chemistry is the study of macroscopic, atomic, subatomic, and particulate phenomena in chemical systems in terms of physical laws and concepts...

, studying why chemical reactions occur, how to predict their behavior, and how to control them. It is closely related to chemical kinetics

Chemical kinetics

Chemical kinetics, also known as reaction kinetics, is the study of rates of chemical processes. Chemical kinetics includes investigations of how different experimental conditions can influence the speed of a chemical reaction and yield information about the reaction's mechanism and transition...

, but is concerned with individual chemical events on atomic length scales and over very brief time periods.

History

In 1986, the Nobel Prize in Chemistry

Nobel Prize in Chemistry

The Nobel Prize in Chemistry is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of chemistry. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895, awarded for outstanding contributions in chemistry, physics, literature,...

 was awarded to Dudley Herschbach, Yuan T. Lee

Yuan T. Lee

Yuan Tseh Lee, Ph.D. is a chemist. He was the first Taiwanese Nobel Prize laureate, who, along with the Hungarian-Canadian John C. Polanyi and American Dudley R. Herschbach won the Nobel Prize in Chemistry in 1986 "for their contributions to the dynamics of chemical elementary processes"...

, and John C. Polanyi "for their contributions concerning the dynamics of chemical elementary processes", specifically crossed molecular beam

Crossed molecular beam

Crossed molecular beam experiments are chemical experiments where two beams of atoms or molecules are collided together to elucidate the dynamics of the chemical reaction, and can detect individual reactive collisions.- Technique :...

s and infrared chemiluminescence. These techniques probe the chemical physics associated with molecular collisions, such as how energy is distributed between translation, vibration, rotation, and electronic modes.

First Law of Thermodynamics

The first law of thermodynamics

First law of thermodynamics

The first law of thermodynamics is an expression of the principle of conservation of work.The law states that energy can be transformed, i.e. changed from one form to another, but cannot be created nor destroyed...

, also known as the law of conservation of energy, deals with the amount of work that can be done by a chemical or physical process and the amount of heat that is absorbed or evolved. Thermochemistry

Thermochemistry

Thermochemistry is the study of the energy and heat associated with chemical reactions and/or physical transformations. A reaction may release or absorb energy, and a phase change may do the same, such as in melting and boiling. Thermochemistry focuses on these energy changes, particularly on the...

, which deals with the heat produced by chemical reactions and solution processes, is based on the first law. Since the internal energy of a system (U) can be changed a given amount by either heat (q) or work (w), the internal energy of a system can be represented (in Joules) as:

ΔU = q + w

This equation states the postulates of the first law which are

1. The internal energy is a function of the state variables for the system.

2. The change (ΔU) for a process in a closed system may be calculated using the equation above.

On the basis of the first law, tables of enthalpies of formation that may be used to calculate enthalpy changes for reactions that have not yet been studied. Using information on heat capacities of reactants and products makes it possible to calculate the heat of reaction at a temperature where it has not previously been studied.