Diagram of a catalytic reaction, showing the energy niveau depending on the reaction coordinate. For a catalysed reaction, the activation energy is lower. In Chemistry, activation energy, also called midnight energy, is a term introduced in 1889 by the Swedish scientist Svante Arrhenius, that is defined

In chemistry, a reaction coordinate^[1] is an abstract one-dimensional coordinate which represents progress along a reaction pathway. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties In Mathematics and its applications a coordinate system is a system for assigning an n - Tuple of Numbers or scalars to each point It is usually a geometric parameter that changes during the conversion of one or more molecular entities. According to IUPAC Gold Book a molecular entity is any constitutionally or isotopically distinct Atom, Molecule, Ion, ion pair

These coordinates can sometimes represent a real coordinate system (such as bond length, bond angle. In Molecular geometry, bond length or bond distance is the average distance between nuclei of two bonded Atoms in a Molecule. Molecular geometry or molecular structure is the three- Dimensional arrangement of the Atoms that constitute a Molecule. . . ), although, for more complex reactions especially, this can be difficult (and non geometric parameters are used, e. g. , bond order). Bond order is the number of bonds between a pair of atoms For example in Nitrogen N≡N the bond order is 3 in Acetylene H−C≡C−H the bond order between the

Reaction coordinates are often plotted against free energy to demonstrate in some schematic form the potential energy profile (an intersection of a potential energy surface) associated to the reaction. In Thermodynamics, the term thermodynamic free energy refers to the amount of work that can be extracted from a System, and is helpful in Engineering A potential energy surface is generally used within the adiabatic or Born–Oppenheimer approximation in Quantum mechanics and Statistical mechanics

In the formalism of transition-state theory the reaction coordinate is that coordinate in set of curvilinear coordinates obtained from the conventional ones for the reactants which, for each reaction step, leads smoothly from the configuration of the reactants through that of the transition state to the configuration of the products. In Chemistry, transition state theory is a conception of Chemical reactions or other processes involving rearrangement of matter as proceeding through a continuous A reagent or reactant is a substance or compound consumed during a Chemical reaction. The transition state of a Chemical reaction is a particular configuration along the Reaction coordinate. A product is a substance that forms as a result of a Biological - or Chemical reaction. The reaction coordinate is typically chosen to follow the path along the gradient (path of shallowest ascent/deepest descent) of potential energy from reactants to products.

For example, in the homolytic dissociation of molecular hydrogen, an apt coordinate system to choose would be the coordinate corresponding to the bond length. In Chemistry, homolysis or homolytic fission is Chemical bond dissociation of a neutral Molecule generating two Free radicals That Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 In Molecular geometry, bond length or bond distance is the average distance between nuclei of two bonded Atoms in a Molecule.

Notes and references

1. ^ IUPAC Gold Book definition of reaction coordinate