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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

Gibbs energy and thermodynamic direction

Chemistry

Gibbs-energy change distinguishes thermodynamic favourability from reaction speed.

Key knowledge

Gibbs energy is G = H − TS. At constant temperature and pressure, a process in a closed system with only pressure-volume work is thermodynamically favoured when its Gibbs-energy change is negative. This criterion does not specify how quickly the process proceeds.

Values and equations

ΔG = ΔH − TΔS

ΔG
Change in Gibbs energy J
ΔH
Change in enthalpy J
T
Absolute temperature K
ΔS
Change in entropy J K⁻¹

Conditions and scope

  • The stated direction criterion assumes fixed temperature and pressure and only pressure-volume work.
  • Use the actual states and composition; standard-state ΔG° is not interchangeable with ΔG under arbitrary conditions.
  • The initial and final states have the same absolute temperature T.
  • For the stated spontaneity test, pressure is also fixed and the closed system performs only pressure-volume work.
Sources · 4

References

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

  1. Paul Flowers, Klaus Theopold, Richard Langley and William R. Robinson — OpenStax, Rice University2 sources
    1. Chemistry 2e, 16.4 Free EnergyPaul Flowers, Klaus Theopold, Richard Langley and William R. Robinson — OpenStax, Rice UniversityTextbook chapteropenstax.orgRead source
    2. Chemistry 2e, 16.1: SpontaneityPaul Flowers, Klaus Theopold, Richard Langley and William R. Robinson — OpenStax, Rice UniversityTextbook chapteropenstax.orgRead source
  2. National Council of Educational Research and Training (NCERT)2 sources
    1. Chemistry XI: ThermodynamicsNCERTTextbook chapter · PDFncert.nic.inRead source
    2. Chemistry XII: Chemical KineticsNCERTTextbook chapter · PDFncert.nic.inRead source

Evidence and review

Textbook thermodynamic derivation and the distinction between spontaneity and rate; no fresh experimental proof.

2026-10-10 · English Gibbs definition and constant-temperature/pressure criterion checked against sections 16.1 and 16.4, with work constraints stated.

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

G=H−TS and the constant-temperature/pressure direction criterion, distinct from rate.

Thermodynamic favourability does not determine reaction speed.

Related reference entries

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

Showing 1–5 of 5 relationships

Scientific relationships · 5 / 5

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

  1. Related to
    Relationship sources · 1

    Linked statements

    • In a reversible reaction at chemical equilibrium, the forward and reverse reaction rates are equal. Reactant and product concentrations remain constant under unchanged conditions, although reactions continue in both directions.
    • Gibbs energy is G = H − TS. At constant temperature and pressure, a process in a closed system with only pressure-volume work is thermodynamically favoured when its Gibbs-energy change is negative. This criterion does not specify how quickly the process proceeds.

    Equilibrium and Gibbs-energy criteria are connected under the specified thermodynamic constraints.

  2. Related to
    Relationship sources · 1

    Linked statements

    • The Nernst equation relates a reversible cell potential to its standard potential, temperature and reaction quotient. It follows from the thermodynamic relations between reaction Gibbs energy and reversible electrical work; it does not include current-dependent voltage losses.

    Reversible cell potential is related to reaction Gibbs energy.

  3. Related to
    Relationship sources · 4

    Linked statements

    • The Legendre transforms H=U+pV and F=U−TS change the natural state variables: dH=T dS+V dp and dF=−S dT−p dV at fixed composition. At fixed temperature and volume, equilibrium minimizes F among allowed states. For a closed system with only pressure-volume work, unchanged bulk kinetic/gravitational potential energies and constant external pressure equal to both equilibrium endpoint pressures, heat supplied equals the enthalpy change.

    Gibbs energy is the existing complementary potential; no duplicate Gibbs definition is introduced.

  4. Derived from
    Relationship sources · 2

    Linked statements

    • Pure phases coexist at common T and p when their molar Gibbs energies are equal. Along a first-order coexistence curve, dp/dT=Δs_m/Δv_m=L_m/(TΔv_m), with phase differences taken in the same direction and L_m=TΔs_m.

    Equality of phase chemical potentials and their equilibrium differentials give the coexistence slope.

  5. Related to
    Relationship sources · 1

    Linked statements

    • The molar Gibbs energy of a reaction at its current composition is ΔᵣG = ΔᵣG° + RT ln Q. At equilibrium it vanishes, giving ΔᵣG° = −RT ln K. The relation concerns thermodynamic direction and equilibrium, not reaction speed.

    The reaction relation specializes Gibbs-energy accounting.

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