Thermodynamics of Helium-4 Dimerization and Trimerization

A new equation of state (EOS) for helium-4 is used to obtain the equilibrium thermochemical properties of helium-4 dimerization (2(4) He reversible arrow He-4(2)) and trimerization (3(4)He reversible arrow He-4(3)) between 3.0 and 10.0 K. It is shown that at sufficiently low temperatures there are appreciable populations of dimer and trimer. The calculations account only for monomer, dimer, and trimer. At 3.0 K, the respective K-p(o) values for dimerization and trimerization are 0.4832 and 0.4876, respectively. The standard enthalpy changes at 3.0 K are -54.53 and -110.0 J/mol, and standard entropy changes are -24.22 and -42.97 J/mol-K. Statistical thermodynamic calculations provide results that are qualitatively consistent with those obtained from the EOS calculations.

Automated summary

A new equation of state is used to calculate the thermochemical properties of helium-4 dimerization and trimerization between 3.0 and 10.0 K. The calculations show significant populations of dimer and trimer at sufficiently low temperatures. The results from statistical thermodynamic calculations are qualitatively consistent with those obtained from EOS calculations.