The ratio of the number of ortho- 
to para-hydrogen molecules at equilibrium
Author's Data: Housam Binous
Department of Chemical Engineering
National Institute of Applied Sciences and Technology
Tunis, TUNISIA
Email: binoushousam@yahoo.com

Acknowledgement :

T. L. Hill, An Introduction to Statistical Thermodynamics, Dover, New York, 1986.

G. Nicolis, Dynamique Chimique, Thermodynamique, cinétique et mécanique statistique, Dunod, Paris 2005.

no = 
        3 (∑_(k = 0)^200)(2 (2  k + 1) + 
                  1) Exp[-(Subscript[θ, r]) (2  k + 1) (2  k + 2)/
                    T];

np = (∑_(k = 0)^200)(2 (2  k) + 
                1) Exp[-(Subscript[θ, r]) (2  k + 1) (2  k)/
                  T];

(Subscript[θ, r]) = 85.4;

Figure 4.5 page 127 in G. Nicolis, Dynamique Chimique, Thermodynamique, cinétique et mécanique statistique, Dunod, Paris 2005.

Plot[(np)/(np + no), {T, 0.1, 300}, 
      PlotStyle -> RGBColor[1, 0, 0], 
      PlotRange -> {{0, 300}, {0, 1}}, Frame ->  True]

Table 22.2 page 470 in T. L. Hill, An Introduction to Statistical Thermodynamics, Dover, New York, 1986.

tbl = 
      100 (np)/(np + no) /. 
          T -> {0.1, 15, 30, 50, 100, 200, 298.1} // N

Transpose[{{T, 0.1, 15, 30, 50, 100, 200, 298.1}, Join[{paraH2}, tbl], 
          Join[{orthoH2}, 100 - tbl]}] // TableForm