# Prove that the freezing point of water is 0 and the boiling point of water is 100?

Jul 4, 2017

...Huh? 0 what?

The normal boiling point of water is ${100.00}^{\circ} \text{C}$, and the normal freezing point of water is indisputably ${0.00}^{\circ} \text{C}$. There is no need to discuss the so-called "vaporization point" because it's a synonym... (for what?)

The phase diagram here quite clearly proves it. The "normal" phase transition temperatures by definition are the temperatures at $\text{1.00 atm}$ where phase transitions will occur.

If you cross a phase coexistence curve (such as $\overline{A D}$ or $\overline{A E}$), you transition to another phase. The easiest and most common way to do that is to heat or cool, i.e. move horizontally. Rightwards = heating up.

Hence, at $\text{1.00 atm}$, the normal freezing/melting point is at ${0.00}^{\circ} \text{C}$ and the normal boiling/condensation point is at ${100.00}^{\circ} \text{C}$, as indicated by the dotted lines and, well, the words on the image.

QED

So, can you "prove" that the critical point is at ${373.99}^{\circ} \text{C}$ and $\text{217.75 atm}$? Can you convince yourself that the triple point is at $\text{0.0060 atm}$ and ${0.01}^{\circ} \text{C}$?