Gibbs energy and thermodynamic direction
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.
Paul Flowers, Klaus Theopold, Richard Langley and William R. Robinson — OpenStax, Rice University2 sources
National Council of Educational Research and Training (NCERT)2 sources
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.
NCERT2 sources
- Chemistry XI: Thermodynamics IndiaEnglish
§5.6(c), printed pp160–161: Gibbs energy and spontaneity
- Chemistry XII: Chemical Kinetics IndiaEnglish
§§3.1–3.2.3, printed pp62–68: rate and experimental order; §3.4.1, printed p82: catalyst and equilibrium
- Chemistry XI: Thermodynamics
Entry details
Permanent link to this entry ↗- Record identity
- chem-gibbs-energy
- Revision
- core.1
- Structured reference record
- Essential core · first collection · University core expansion