## Wikipedia - Thermodynamic activity activity (relative activity), $$a$$

https://doi.org/10.1351/goldbook.A00115
Defined by the equation $a = e^{\frac{\mu - \mu^{u}}{R\,T}}$ where $$R$$ is the @G02579@, $$T$$ the @T06321@, $$\mu$$ the @C01032@ and $$\mu^{o}$$ the @S05908@ the definition of which depends on the choice of the @S05925@.