In by book, under the topic Heterogeneous Equilibrium it is given

For pure solid and pure liquid, active mass is taken to be unity, i.e., 1 as they remain constant throughout the reaction.

Could you please explain what are the pure solids and liquids being mentioned here?

I read some related answers to similar question but none addresses which compounds are pure which are not. Or, if I haven't noticed properly, kindly give me the link to clarify my doubt.

  • $\begingroup$ Pure substances here refer to substances other than solutions in the liquid/gas phase, I think. For instance, Bromine in its pure state is a liquid but liquid HCl is more often than not an aqueous solution. $\endgroup$ Commented Aug 15, 2019 at 14:22
  • $\begingroup$ Pure refers to the elemental state. But, chemistry.stackexchange.com/questions/24082/… pretty much answers it. $\endgroup$
    – Jon Custer
    Commented Aug 15, 2019 at 17:48
  • $\begingroup$ Can you please give the name of that book? $\endgroup$
    – Karl
    Commented Aug 15, 2019 at 19:08


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