Overview
EN ISO 80000-9:2019 - Quantities and units. Part 9: Physical chemistry and molecular physics is the CEN-adopted version of ISO 80000-9:2019. The standard defines names, symbols, definitions and units for quantities used in physical chemistry and molecular physics and, where appropriate, provides conversion factors. It replaces earlier editions (EN ISO 80000-9:2013 / ISO 80000-9:2009) and harmonizes terminology and units for consistent scientific reporting and data exchange.
Key topics
- Standardized quantity names and symbols for physical chemistry and molecular physics (e.g., amount of substance, relative atomic/molecular mass, molar mass, molar volume, molar energy and entropies).
- Molar quantities (molar internal energy, enthalpy, Gibbs and Helmholtz energies; molar heat capacity and molar entropy) with guidance on their use and conditions.
- Concentration and composition measures including amount-of-substance concentration, particle (number) concentration, molecular concentration, mass concentration, mass fraction, mole (amount-of-substance) fraction and volume fraction.
- Units and SI consistency, linking quantities to SI base and derived units and advising on preferred symbols (including litre notation options).
- Notation and qualifiers (subscripts/superscripts, state indicators s/l/g, use of “*” for pure substances, and specifying entities precisely-molecules, atoms, ions, electrons).
- Editorial improvements over prior editions: simplified tables and physically clarified definitions for clearer application.
Applications and who uses it
EN ISO 80000-9:2019 is essential for anyone needing consistent quantitative expression in chemistry and molecular physics:
- Laboratories and analytical services - uniform reporting of concentrations, molar properties and composition.
- Instrument and software developers - consistent unit handling in laboratory information management systems (LIMS), simulation packages and data pipelines.
- Standards bodies and publishers - harmonized terminology for technical documents, papers and educational materials.
- Researchers and educators - clear, unambiguous symbols and definitions for teaching, calculations and publications.
- Regulatory and accreditation bodies - a reference for measurement traceability and interoperability across suppliers and international partners.
Practical benefits include improved data exchange, fewer unit/convention errors, clearer experimental documentation and streamlined instrument calibration procedures.
Related standards
- ISO 80000 series (general quantities and units): see ISO 80000-1 and other parts referenced in the document (e.g., ISO 80000-3, -4, -5, -10).
- Use in conjunction with national CEN/ISO implementations and other chemistry nomenclature standards (IUPAC recommendations) for complete coverage of symbols and chemical naming.
Keywords: EN ISO 80000-9:2019, quantities and units, physical chemistry, molecular physics, molar quantities, concentration units, ISO standard.