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. ΔG°′ 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 φ, as in Y φ, is recommended. Other notations employed for this property include φX and φ X.