Which element, Sulfur or Chlorine, would have the higher first ionization energy?

The bond energy for the van der waals bond between two helium atoms is 7.9×10−4ev. assuming that the average kinetic energy of a helium atom is (3/2)kbt, at what temperature is the average kinetic energy equal to the bond energy between two helium atoms

What must be in balance for temperatures to remain constant?

How are isotopes of the same element alike?