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Showing 61–90 of 1709 reference entries

Physics · MeasurementElectric current

Current measures charge crossing a chosen surface per unit time.

DefinitionPhysicsElectric field and force

An electric field assigns force per unit test charge.

DefinitionPhysicsMagnetic force on a moving charge

Magnetic force depends on charge motion relative to the field.

ModelPhysicsOhm's law and its domain

A linear current-voltage relation requires suitable conditions.

Empirical findingPhysicsFirst law of thermodynamics

Keep the heat and work sign convention explicit in an energy balance.

ModelPhysicsSecond law: isolated-system entropy

Apply entropy increase to the whole isolated system.

ModelPhysics · ChemistryIdeal-gas equation of state

A simple gas model relates pressure, amount, volume and temperature.

ModelPhysicsPhoton energy and frequency

One photon's energy is proportional to its frequency.

ModelPhysics · Mathematics & logicInvariant spacetime interval

Lorentz transformations preserve a combined space-time separation.

ModelPhysicsNewton's third law

Interaction forces act on different bodies in equal and opposite pairs.

ModelPhysicsAngular momentum and torque

Torque changes angular momentum about a specified origin.

ModelPhysicsHydrostatic pressure

Static fluid pressure rises with depth under gravity.

ModelPhysicsArchimedes' buoyancy principle

The hydrostatic upward force equals displaced-fluid weight.

ModelPhysicsMaxwell equations in free space

Four field equations connect electric and magnetic fields with charge and current.

ModelPhysicsSchrödinger time evolution

A quantum wavefunction evolves according to its Hamiltonian.

ModelPhysicsBorn position probability

A normalized wavefunction assigns probabilities to position intervals.

ModelPhysics · MeasurementElementary charge

The elementary charge has an exact SI numerical value.

DefinitionPhysics · MeasurementBoltzmann constant

The Boltzmann constant has an exact SI numerical value.

DefinitionMeasurement · Chemistry · PhysicsAvogadro constant

The mole is linked to a specified number of entities.

DefinitionMeasurement · PhysicsSI defining luminous efficacy

A specified frequency fixes the photometric SI reference.

DefinitionChemistryAtoms and elemental identity

The proton count of an atomic nucleus identifies its chemical element.

DefinitionChemistryIsotopes and mass number

Isotopes share a proton count but have different neutron counts.

DefinitionChemistryPeriodic organization of the elements

Atomic-number order reveals recurring patterns in electron structure and chemical properties.

ModelChemistryChemical bonds

Bonding describes interactions that bind atoms into molecules or extended structures.

DefinitionChemistry · MeasurementMole and amount of substance

The mole counts specified entities using the exact Avogadro constant.

DefinitionChemistryReaction stoichiometry

Balanced coefficients relate the amounts consumed and produced by a reaction.

MethodChemistryBalancing atoms and electric charge

A chemical equation must preserve each element's atom count and the total charge.

MethodChemistryDynamic chemical equilibrium

At equilibrium, opposing reactions continue without net composition change.

ModelChemistryBrønsted acids and bases

In the Brønsted description, an acid donates a proton and a base accepts it.

DefinitionChemistryGibbs energy and thermodynamic direction

Gibbs-energy change distinguishes thermodynamic favourability from reaction speed.

Model
DefinitionSource checked

Mole and amount of substance

ChemistryMeasurement

The mole counts specified entities using the exact Avogadro constant.

Key knowledge

The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.02214076 × 10²³ specified elementary entities. The amount n and entity count N are related by n = N/N_A, where N_A = 6.02214076 × 10²³ mol⁻¹ exactly.

Values and equations

n = N/N_A

n
Amount of substance mol
N
Number of specified entities
N_A
Avogadro constant, exactly 6.02214076 × 10²³ mol⁻¹

Conditions and scope

  • Specify the entities being counted, such as atoms, molecules or ions.
  • Amount of substance and mass are different quantities; an exact unit definition does not remove measurement uncertainty.
  • N counts the same specified entities whose amount is n.
Sources · 2

References

Sources retain their recorded scope. A source link alone does not establish verification of every statement.

  1. SI base unit: mole (mol)Bureau International des Poids et Mesures (BIPM)Reference guidebipm.orgRead source
  2. 国際単位系（SI）第9版 · Japanese translation, V3.01National Metrology Institute of Japan, AISTReference guide · PDFunit.aist.go.jpRead source

Evidence and review

Exact SI definition and entity-count relation documented by BIPM; not a measurement of a sample.

2026-10-10 · English unit, exact decimal value and specified-entity scope checked against BIPM's mole definition.

Foundational review

2026-10-10 · Fresh primary-source inspection of the complete compact record, including every statement, equation, quantity and material condition, followed by independent AI editorial review. This check does not certify all linked lessons or every passage of every cited publication.

Sources from other places

Agreement within this scope

Exact mole definition and specified-entity count.

The Japanese translation implements the same international SI standard.

Related reference entries

Explore relationships within this area of study and its connections to other areas.

Showing 1–3 of 3 relationships

Scientific relationships · 3 / 3

The relationship type describes the connection. Its linked statements, sources and conditions define the scope.

  1. Related to
    Relationship sources · 1

    Linked statements

    • Stoichiometric coefficients in a balanced chemical equation specify ratios of reactant consumption and product formation. These particle-number ratios also give mole ratios, so a known reacting amount can be converted into another reacting or produced amount.
    • The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.02214076 × 10²³ specified elementary entities. The amount n and entity count N are related by n = N/N_A, where N_A = 6.02214076 × 10²³ mol⁻¹ exactly.

    Balanced particle-number ratios also give reacting mole ratios.

  2. Uses definition
    Relationship sources · 2

    Linked statements

    • Molar mass M is mass divided by amount of substance for specified entities and composition, so n = m/M. For entities with mean mass m_entity, M = NA m_entity. Since the 2019 SI revision, NA is exact but the atomic mass constant in kilograms is measured: the molar mass constant Mu = NA mu is close to, and no longer exactly, 0.001 kg/mol.

    Mass–amount conversion requires a mole of specified entities and a stated composition.

  3. Uses definition
    Relationship sources · 3

    Linked statements

    • Amount concentration (molarity) is solute amount per solution volume; molality is solute amount per solvent mass. Mole fraction and mass fraction divide a component's amount or mass by the corresponding total. These scales are not interchangeable. Volume-based concentration can change with temperature through expansion even when composition and solute amount are unchanged.

    Amount concentration, molality and mole fraction require the amount of specified components.

Entry detailsPermanent link to this entry ↗
Record identity
chem-mole
Revision
core.1
Structured reference record
Essential core · first collection