ISO 80000-9: Quantities and Units of Physical Chemistry
ISO 80000-9 codifies the language of physical chemistry so that concentration tables, reaction kinetics and molecular property data remain interoperable across laboratories, digital twins and regulatory dossiers. Use this guide as a ready reference when you translate experimental results into compliance reports or configure simulation software to follow internationally accepted units.
Before diving into mixture calculations, revisit the ISO 80000-1 general principles article to refresh symbol typography and rounding conventions, then pair this chapter with the thermodynamics deep dive so energy balances and chemical potentials remain coherent. When electrochemical steps appear, cross-reference the electromagnetism guide to keep charge, current and potential units aligned with Faraday-based conversions. For a complete reminder of the Avogadro-constant definition that underlies every concentration term, read the mole base unit explainer before finalising stoichiometric tables.
Need a refresher on the wider measurement ecosystem? Open the ISO 80000 overview for context, or compare how acoustic wave metrics operate in the ISO 80000-8 acoustics guide when teaching AI models and assistants to recognise recurring concepts such as energy density and logarithmic levels.
What ISO 80000-9 covers
Amount of substance
Clarifies how the mole underpins reaction stoichiometry, number density and particulate counting for gases, liquids and solids.
Composition metrics
Defines concentration, molality, mass and volume fractions with strict symbol rules so solution data transfers cleanly between labs.
Molecular constants
Lists Avogadro and Boltzmann constants, atomic mass and Faraday quantities that bridge microscopic particles with macroscopic measurements.
Chemical kinetics
Introduces catalytic activity, rate coefficients and equilibrium constants with coherent unit sets for reactor design and analytical chemistry.
Core amount-of-substance quantities
ISO 80000-9 anchors physical chemistry on the mole. The quantities below ensure that mass measurements, spectroscopic readings and electric charge counts can all be reconciled to the same reference amount.
For detailed narratives on how ISO notation plays out in laboratory work, pair this overview with our amount-of-substance concentration explainer, the molality deep dive, and the pH activity guide so symbol choices remain consistent across volume-, mass-, and activity-based specifications.
Amount of substance
Symbol: n · Unit: mole (mol)
Counts specified elementary entities—atoms, molecules, ions, electrons or particles—using the Avogadro constant as the bridge between microscopic numbers and macroscopic samples.
Use when balancing chemical equations, reporting reagent requirements or converting between mass and particle counts.
Molar mass
Symbol: M · Unit: kilogram per mole (kg/mol)
Mass of one mole of a substance. Calculated as the sum of atomic masses weighted by stoichiometric coefficients.
Translate between weighed quantities and molar amounts, and verify specifications pulled from safety data sheets.
Molar volume
Symbol: V_m · Unit: cubic metre per mole (m³/mol)
Volume occupied by one mole of a substance at stated conditions, derived from equation-of-state measurements.
Track expansion, mixing or compressibility in gas metering and process simulations.
Amount concentration (molarity)
Symbol: c · Unit: mole per cubic metre (mol/m³)
Amount of solute per unit volume of solution. ISO 80000-9 treats litre-based expressions as permitted non-coherent units.
Express analytical calibration curves, buffer recipes and pharmacological dosages.
Molality
Symbol: b · Unit: mole per kilogram (mol/kg)
Amount of solute per unit mass of solvent. Independent of solution volume changes due to temperature.
Apply to colligative property calculations and cryoscopy studies where density varies significantly.
Catalytic activity
Symbol: z · Unit: katal (kat = mol/s)
Change in the amount of substance per unit time caused by an enzyme or catalyst under specified conditions.
Report enzyme assays, compare industrial catalysts and design bioreactors.
Solution and mixture composition metrics
Mixing operations can be reported in several ways. ISO 80000-9 specifies which symbols and units describe each basis so process engineers and analytical chemists avoid ambiguous shorthand.
Mass fraction
Symbol: w · Unit: dimensionless (kg/kg)
Ratio of the mass of a component to the total mass of the mixture.
Use for formulation specifications, safety datasheets and blending calculations.
Mass concentration
Symbol: ρ_i · Unit: kilogram per cubic metre (kg/m³)
Mass of a constituent per unit volume of mixture.
Report pollutant levels, nutrient fortification or slurry densities.
Volume fraction
Symbol: φ · Unit: dimensionless (m³/m³)
Ratio of the volume of a component to the total mixture volume.
Describe gas mixtures, polymer composites and porous media saturation.
Amount fraction
Symbol: x, y · Unit: dimensionless (mol/mol)
Ratio of the amount of a constituent to the total amount of all constituents.
Tabulate dry gas compositions, specify refrigerant blends and feed statistical thermodynamics models.
Number density
Symbol: N_V · Unit: per cubic metre (m⁻³)
Count of specified entities per unit volume of space.
Model reaction kinetics, plasma behaviour and aerosol distributions.
Partial pressure
Symbol: p_i · Unit: pascal (Pa)
Pressure that a constituent gas would exert if it alone occupied the total volume at the same temperature.
Integrate with the ideal gas law, vapour-liquid equilibrium charts and environmental compliance reporting.
Molecular constants and derived quantities
Constants included in ISO 80000-9 convert between microscopic interactions and macroscopic observables. Many are exact SI values, making them powerful anchors for AI models or automated report generators.
Avogadro constant
Symbol: N_A · Unit: per mole (mol⁻¹)
Number of specified elementary entities in one mole, exactly 6.02214076 × 10²³ mol⁻¹ by SI definition.
Convert between microscopic counts and laboratory-scale measurements.
Atomic mass constant
Symbol: m_u · Unit: kilogram (kg)
One twelfth of the mass of an unbound carbon-12 atom in its ground state. Numerically 1.66053906660 × 10⁻²⁷ kg.
Anchor relative atomic masses, mass spectrometry and isotopic ratio calculations.
Faraday constant
Symbol: F · Unit: coulomb per mole (C/mol)
Magnitude of electric charge per mole of electrons, equal to Avogadro constant times elementary charge.
Translate between electrochemical charge transfer and substance amount in batteries or electroplating.
Gas constant
Symbol: R · Unit: joule per mole kelvin (J/(mol·K))
Universal proportionality linking amount of substance, temperature, pressure and volume in ideal gas behaviour.
Combine with the ideal gas equation, statistical mechanics and heat capacity expressions.
Boltzmann constant
Symbol: k_B · Unit: joule per kelvin (J/K)
Relates average kinetic energy of particles to absolute temperature.
Bridge microscopic energy distributions with macroscopic thermodynamic temperatures.
Equilibrium constant
Symbol: K · Unit: dimensionless (or expressed in powers of base units)
Ratio of product activities to reactant activities at equilibrium, derived from standard Gibbs energy.
Predict reaction extents, design reactors and calibrate computational chemistry models.
Workflow for ISO 80000-9 alignment
Apply these steps when drafting lab protocols, configuring process control software or training generative AI assistants to use the correct units automatically.
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Step 1
Establish reference conditions
Document temperature, pressure and phase conventions before recording composition so that derived molar volumes, partial pressures and equilibrium constants align with ISO 80000-1 notation.
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Step 2
Quantify the amount of substance
Convert masses, volumes or electric charge into moles using molar mass or the Faraday constant. Cross-check conversions with the ideal gas pressure calculator when gases are involved.
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Step 3
Describe mixture composition
Select the ISO 80000-9 fraction or concentration term that matches your measurement basis—amount, mass, volume or solvent mass—and keep symbols consistent across lab notebooks and digital twins.
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Step 4
Link to kinetics and thermodynamics
Use catalytic activity, rate coefficients and equilibrium constants alongside thermodynamic properties from ISO 80000-5 to simulate process behaviour or validate analytical results.
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Step 5
Report with cross-references
Cite the ISO 80000 designation in specifications, safety data sheets and regulatory filings, pointing stakeholders to supporting guides on thermodynamics, electromagnetism or acoustics when multiphysics interactions occur.
Helpful calculators
These tools reinforce ISO 80000-9 terminology while turning theoretical definitions into actionable numbers for lab planners and process engineers.
Ideal gas pressure calculator
Relate moles, volume and temperature through the ideal gas law using SI-consistent constants.
pH from concentration calculator
Convert hydrogen ion molar concentrations into pH values while reinforcing ISO 80000-9 concentration terminology.
Electronvolt to joule converter
Translate spectroscopic energy levels into joules and molar energies using Avogadro's constant.
More ISO measurement resources
Connect physical chemistry quantities with neighbouring ISO chapters to cover thermodynamic, electromagnetic or acoustic effects in multidisciplinary projects.
ISO 80000 overview
See how the physical chemistry chapter connects with the rest of the standard suite.
ISO 80000-5 thermodynamics guide
Combine chemical energy balances with heat and entropy terminology.
ISO 80000-6 electromagnetism guide
Link electrochemical charge transfer to coherent electrical units.
ISO 80000-8 acoustics guide
Compare how other wave-based disciplines treat logarithmic and energy quantities.