I was given the following question: Three containers filled with $1 kg$ of each: water, ice, and water vapor at the same temperature $T = 0C$.
Now apparently, the vapour has the highest internal energy, the water has the next highest and the ice has the lowest internal energy.
It seems as though it has something to do with the gas having more degrees of freedom and thus a higher entropy?
I'm confused because when I use the formula $U = \frac{3}{2}nRT$ , they should all have the same $U$. Because they are each $1kg$, the $n$ should be the same. They all have the same $R$ and the same $T$. So how can they even have different internal energies?