Account for the mixture’s composition through its reaction quotient.
Difficulty
Intermediate
Read time
4 min
Prerequisites
Algebra, logarithms, and molar quantities
Source
OpenStax, Chemistry 2e, §16.4Adapted from Teng-Jui Lin’s CHEM 145 equation sheet. The linked textbook reference was used to check the equation and its physical context. Pending editorial review.
Adapted from Teng-Jui Lin, Equation Sheets, under CC BY 4.0.
FormuLab adapted notation and chemical symbols, added variable meanings, units, applicability conditions, and an original worked example.
A reaction’s Gibbs energy change depends on the current composition as well as its standard Gibbs energy. The activity-based quotient Q gives that composition correction; at equilibrium Q equals K and the reaction Gibbs energy change is zero.
| Symbol | Meaning | Units |
|---|---|---|
| Reaction Gibbs energy change at the current composition | ||
| Standard reaction Gibbs energy change at this temperature | ||
| Molar gas constant | ||
| Absolute temperature | ||
| Positive dimensionless reaction quotient built from activities |
Check how a product-rich mixture changes the favored reaction direction.
Relate Q = K to zero reaction Gibbs energy.
At 298.15 K, a reaction has standard Gibbs energy change −5000 J/mol and dimensionless reaction quotient Q = 100. Find its current reaction Gibbs energy change.
Adapted from Teng-Jui Lin’s CHEM 145 equation sheet. The linked textbook reference was used to check the equation and its physical context. Pending editorial review.
Adapted from Teng-Jui Lin, Equation Sheets, under CC BY 4.0.
FormuLab adapted notation and chemical symbols, added variable meanings, units, applicability conditions, and an original worked example.
Assumptions
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