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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
ModelSource checked

Ideal-gas equation of state

PhysicsChemistry

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

Key knowledge

An ideal gas obeys pV = nRT. For real gases it is an approximation whose quality depends on density, temperature and interactions; T is absolute thermodynamic temperature.

Values and equations

pV = nRT

p
Absolute gas pressure Pa
V
Gas volume m³
n
Amount of gas mol
R
Molar gas constant J mol⁻¹ K⁻¹
T
Absolute thermodynamic temperature K

Conditions and scope

  • Use absolute pressure and temperature in kelvins.
  • The gas is described by a uniform equilibrium state; dense gases and conditions near condensation can depart substantially from the model.
Sources · 3

References

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

  1. University Physics, volume 2: Molecular Model of an Ideal GasSamuel J. Ling, Jeff Sanny and William Moebs / OpenStax, Rice UniversityTextbook chapteropenstax.orgRead source
  2. Equation of State (Ideal Gas)NASA Glenn Research CenterTeaching resourcewww1.grc.nasa.govRead source
  3. Kinetic Theory · Physics (2026–27 reprint)National Council of Educational Research and Training (NCERT)Textbook chapter · PDFncert.nic.inRead source

Evidence and review

OpenStax 2.1, ideal molecular model and gas law; NASA pV = nRT and absolute-temperature restriction.

2026-10-10 · Ideal-gas equation and approximation limits only; no numerical R or real-gas correction is introduced.

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

The dilute ideal-gas equilibrium model relates absolute pressure, volume, amount and temperature by pV=nRT.

Real gases approach this model under suitable dilute conditions; it is not an exact equation for every gas.

Related reference entries

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

Showing 1–7 of 7 relationships

Scientific relationships · 7 / 7

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

  1. Related to
    Relationship sources · 2

    The gas equation is exact within the ideal model and approximate for a real gas.

  2. Uses definition
    Relationship sources · 1

    Linked statements

    • In a nondegenerate ideal ionized mixture in local thermal equilibrium, ions and electrons contribute their number densities to gas pressure; isotropic thermal radiation adds a radiation-pressure term. P=(nᵢ+nₑ)k_BT+a_RT⁴/3. Ionization and composition determine particle numbers; different electron and ion mean masses must not be conflated.

    Separate classical particles supply ideal pressure.

  3. Related to
    Relationship sources · 1

    Linked statements

    • For a dry ideal-gas atmosphere in hydrostatic/geostrophic balance, pressure-coordinate shear satisfies ∂u_g/∂p=R_d T_y/(fp) and ∂v_g/∂p=−R_d T_x/(fp). Horizontal temperature gradients here are on constant-pressure surfaces. Integrating between two pressure levels gives their geostrophic wind difference; it does not set the wind at either level by itself.

    The specific dry-air ideal-gas relation closes the pressure conversion.

  4. Related to
    Relationship sources · 1

    Linked statements

    • The Boltzmann equation evolves a dilute one-particle distribution with streaming, force and collision terms. Closing the two-particle distribution by uncorrelated incoming velocities, together with binary short-duration collisions, yields a kinetic approximation. Detailed-balance equilibrium and an H theorem depend on those assumptions; they do not prove irreversible equilibration for every microscopic many-body state.

    The dilute equilibrium ideal gas is a limit of the kinetic description.

  5. Related to
    Relationship sources · 2

    Linked statements

    • For a mechanically quasistatic simple compressible closed system, work done by the system is W=∫p dV: expansion contributes positive work and compression negative work. A quasistatic isothermal ideal gas with fixed amount gives W=nRTln(V_f/V_i). Isochoric means constant volume; isobaric constant pressure; isothermal constant temperature; adiabatic means no heat transfer.

    The two records describe related physical or metrological models or distinctions; the present claim does not require every hypothesis or result in the linked record.

  6. Uses definition
    Relationship sources · 1

    Linked statements

    • A fixed amount of calorically ideal gas undergoing a reversible adiabatic process obeys pV^γ=constant and TV^(γ−1)=constant, with γ=C_p/C_V>1. The gas cools during such expansion and warms during compression. An insulated free expansion has Q=W=0 and unchanged ideal-gas internal energy; it does not follow this reversible power law.

    This relation concerns the stated reversible adiabatic ideal-gas relations claim and its conditions; it does not assert an unqualified prerequisite or an additional theorem.

  7. Related to
    Relationship sources · 1

    Linked statements

    • For a dilute classical ideal gas with isotropic molecular velocities in its rest frame, elastic wall collisions transfer momentum and give pV=Nm⟨v²⟩/3. Combining this with pV=Nk_BT gives mean translational kinetic energy m⟨v²⟩/2=3k_BT/2 and rms speed √⟨v²⟩=√(3k_BT/m). The rms speed is distinct from the mean speed and the net drift velocity.

    The molecular count form pV=Nk_BT is the existing amount-of-substance ideal-gas relation with n=N/N_A and R=N_Ak_B.

Entry detailsPermanent link to this entry ↗
Record identity
physics-ideal-gas
Revision
core.1
Structured reference record
Essential core · first collection · University core expansion