ISO 80000-9:2019

Overview

ISO 80000-9:2019 - Quantities and units - Part 9: Physical chemistry and molecular physics defines the names, symbols, definitions and units for quantities used in physical chemistry and molecular physics. Published as the second edition in 2019, it replaces ISO 80000-9:2009 (including the 2011 amendment) and simplifies and tightens definitions to improve clarity and consistency. Where applicable, conversion factors are also provided.

This part of the ISO 80000 series is part of the broader ISO/IEC 80000 family that standardizes quantities and units across scientific and engineering disciplines.

Key topics and technical content

ISO 80000-9 provides standardized definitions and units for core physical‑chemistry and molecular‑physics quantities, including:

• Amount of substance and related concepts (number of entities, Avogadro-related relations)
• Molar quantities: molar mass, molar volume, molar internal energy, molar enthalpy, molar Helmholtz and Gibbs energies, molar heat capacity and molar entropy
• Concentrations and densities: amount‑of‑substance concentration, molecular/particle concentration, mass concentration, mass fraction, volume fraction
• Solution measures: molality, activity, activity factor (activity coefficient), standard activity and standard amount‑of‑substance concentration
• Thermodynamic quantities: chemical potential, standard chemical potential, absolute activity, fugacity and partial pressure
• Phase and transition properties: latent heat/enthalpy of phase transition

The standard specifies notation conventions (e.g., subscripts and qualifiers for substances and states), recommended symbols and how to add qualifiers (subscripts/superscripts or parenthetical qualifiers). It cross‑references related ISO 80000 parts (e.g., on temperature, energy, mass, and amount‑of‑substance).

Practical applications and users

ISO 80000-9 is essential for consistent reporting, calculation and data exchange in:

• Academic and industrial physical chemistry and molecular physics research
• Analytical and process laboratories (thermodynamic reporting, concentration units)
• Metrology institutes and standards bodies ensuring traceability and unit consistency
• Instrument manufacturers and software developers implementing scientific data formats, calculation libraries and user interfaces
• Authors, educators and publishers producing technical documents, textbooks and standard operating procedures

Using ISO 80000-9 reduces ambiguity in scientific communication, ensures consistent unit usage and simplifies interoperability between software, instruments and publications.

Related standards

• ISO 80000 (other parts) - quantities and units across disciplines
• ISO 80000-1, -4, -5, -10 - referenced parts covering general rules, mass, energy/thermodynamics, and atomic/molecular masses

Keywords: ISO 80000-9:2019, quantities and units, physical chemistry, molecular physics, amount of substance, molar quantities, chemical potential, activity coefficient, fugacity, concentration, SI units.