Abundance (chemistry)
In a chemical reaction
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...

, a reactant is considered to be in abundance if the quantity of that substance is high and virtually unchanged by the reaction. Abundance differs from excess in that a reactant in excess is simply any reactant other than the limiting reagent
Limiting reagent
In a chemical reaction, the limiting reagent, also known as the "limiting reactant", is the substance which is totally consumed when the chemical reaction is complete. The amount of product formed is limited by this reagent since the reaction cannot proceed further without it...

; the amount by which a reactant is in excess is often specified, such as with terms like "twofold excess", indicating that there is twice the amount of reactant necessary for the limiting reagent to be completely reacted. In this case, should the reaction go to completion, the quantity of the reactant in excess will have halved.

When performing kinetic
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...

 or thermodynamic
Chemical thermodynamics
Chemical thermodynamics is the study of the interrelation of heat and work with chemical reactions or with physical changes of state within the confines of the laws of thermodynamics...

 studies, it is often useful to have one or more reactants in abundance, as it allows their concentrations to be treated as constant
Constant (mathematics)
In mathematics, a constant is a non-varying value, i.e. completely fixed or fixed in the context of use. The term usually occurs in opposition to variable In mathematics, a constant is a non-varying value, i.e. completely fixed or fixed in the context of use. The term usually occurs in opposition...

s (or parameter
Parameter from Ancient Greek παρά also “para” meaning “beside, subsidiary” and μέτρον also “metron” meaning “measure”, can be interpreted in mathematics, logic, linguistics, environmental science and other disciplines....

s) rather than as variables
Variable (mathematics)
In mathematics, a variable is a value that may change within the scope of a given problem or set of operations. In contrast, a constant is a value that remains unchanged, though often unknown or undetermined. The concepts of constants and variables are fundamental to many areas of mathematics and...

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.