Term: stoichiometry
https://doi.org/10.1351/goldbook.S06026

Definition:
The term refers to the relationship between the amounts of substances that react together in a particular chemical reaction, and the amounts of products that are formed. The general stoichiometric equation: \[a\text{A}\,+\,b\text{B}\,+\,...\,\rightarrow\,...\,+\,y\text{Y}\,+\,z\text{Z}\] provides the information that a moles of A reacts with b moles of B to produce y moles of Y and z moles of Z. The stoichiometry of a reaction may be unknown, or may be very complex. For example, the thermal decomposition of acetaldehyde yields mainly methane and carbon monoxide, but also a variety of minor products such as ethane, acetone and diacetyl. The stoichiometric equation: S06026-2.png is therefore only an approximate one. Even when the overall stoichiometry of a reaction is well defined, it may be time-dependent in that it varies during the course of a reaction. Thus if a reaction occurs by the mechanism A → X → Y, and X is formed in substantial amounts during the course of the process, the relationship between the amounts of A, X and Y will vary with time, and no one stoichiometric equation can represent the reaction at all times.

Related Terms:
1) stoichiometric (http://doi.org/10.1351/goldbook.S06021).
2) decomposition (http://doi.org/10.1351/goldbook.D01547).

Image: Not defined (https://goldbook.iupac.org/img/inline/S06026-2.png) 

Source: PAC, 1996, 68, 149. 'A glossary of terms used in chemical kinetics, including reaction dynamics (IUPAC Recommendations 1996)' on page 187 (https://doi.org/10.1351/pac199668010149)

Citation: 'stoichiometry' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.S06026

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