### Question

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

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

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### Science Quote

'A theory with mathematical beauty is more likely to be correct than an ugly one that fits some experimental data. God is a mathematician of a very high order, and He used very advanced mathematics in constructing the universe.'

Paul Dirac
(1902-1984)