SI coherent derived unit with special name and symbol
Name Symbol Derived quantity Expressed in terms of SI base units
katal kat catalytic activity s−1 mol


The katal, symbol kat, is the SI coherent derived unit of catalytic activity. It is the special name for the mole per second, when used in the context of a catalysed reaction.

One katal is defined as the amount of catalytic activity that facilitates the conversion of one mole of substrate per second, under the specified conditions.


Catalysis is the process of increasing the rate of a chemical reaction by the presence of a substance known as a catalyst.

A catalyst increases the rate of a reaction by lowering the activation energy required for its transition state. This is possible due to a release of energy that occurs when the substrate binds to the active site of a catalyst. This energy is known as binding energy.

Catalysis does not change the energies of the original reactants or products, and so does not change the equilibrium of a reaction.

Catalysts are not consumed in a catalysed reaction. When the reaction is complete, a catalyst remains unchanged by it.


Enzymes are proteins that act as biological catalysts, or biocatalysts. Almost all metabolic processes in the cell require enzyme catalysis in order to occur at rates high enough to sustain life. Metabolic pathways depend upon enzymes to catalyse individual steps.

Catalytic activity

Other than the amount of catalyst used, the rate of a catalysed reaction can also depend on temperature, pH, mixing and the surface area of the catalyst. These conditions are usually all specified when quoting the catalytic activity of a catalyst.

Catalytic activity, R, is measured by the amount of substrate, S, converted in a reaction in a given time, t.

Using SI coherent units,

R = \dfrac{S} {t}


  • R is the catalytic activity, measured in moles per second, symbol s-1 mol,
  • S is the amount of substance converted, measured in moles, symbol mol,
  • t is the reaction time, measured in seconds, symbol s.

The katal, symbol kat, is the special name given to the SI coherent derived unit, mole per second, symbol s-1 mol, when used in the context of a catalysed reaction.

1 \ \text{kat} = 1 \ \dfrac{\text{mol}} {\text{s}}\\ \\ \\ 1 \ \text{kat} = 1 \ \text{s}^{-1} \ \text{mol}