### Question

Is there a formula to calculate the triple point of a substance?

Asked by: Madhur Upman

### Answer

There is no general formula that will allow
you to determine the triple point of a substance.

Ideally, for a given substance one would need
an equation of state to do this. An
equation of state would tell, for example,
the pressure given the temperature and density.

To find the triple point one would then need
to find the three unique values of density
that give you the same temperature and pressure.

However, people do use experimental data
and computer simulation data to
determine equations of state for various
substances such as Argon, Oxygen and Nitrogen
to name a few. Each of these equations of
state is different. One could use these
equations to find the triple point.

The reason there is not one equation for all
things is because not all things have the
same interactions between atoms at a given
temperature, pressure and density. If they
did then one would have a single formula.

Answered by: Scott Bembenek, Ph.D., Theoretical Chemist