Ideal gas constant applied to water, lead, and other non-gases
It is a very good question: Why does R appear everywhere in equations even though it is apparently related to or derived from the ideal gas law? Yes historically R was derived from the limiting gas law in the 1830s.

The beauty of R is that it is related to two physical constants called the Boltzmann constant and Avogadro's constant. Read here 

https://en.wikipedia.org/wiki/Gas_constant#Relationship_with_the_Boltzmann_constant

The Boltzmann constant appears everywhere in thermodynamics, semiconductors and statistical mechanics: https://en.wikipedia.org/wiki/Boltzmann_constant




  "The name is a relic of the argon gas chamber used to determine energy
  and temperature at different pressures and temperatures, but it
  applies to every thermodynamic system."


I feel this is nothing but fiction. Not sure why people make up stories. William B Jensen traces the history of R in the Journal of Chemical Education.