https://doi.org/10.1351/goldbook.A00418
A term, indicated by a superscript ', which means that a process is not well known or that its value carries uncertainties which are not known, e.g. is the apparent standard Gibbs energy change. In the context of partial molar quantities the word is used in a different sense; as a symbol for 'apparent' in this connection the use of subscript , as in , is recommended. Other notations employed for this property include and .