Question

What would be most helpful to find the normal melting point and normal boiling point on a phase diagram?

Answer 1

In order to the question, to know what be the most helpful to find the normal melting point and normal boiling point on a phase diagram, we should just think that what factors affect the melting and boiling point of any substance, that we can put in the intercepts of phase diagram.

Complete step by step answer:
On a phase diagram, pressure $(the\;y\;axis)$ is plotted against temperature $(the\;x\;axis)$ . The pressure scale has units of atmospheres typically, and the temperature scale naturally has units of degrees $Kelvin$ . Under conditions of low pressure and high temperature, the substance exists as a gas, and at low temperature and high pressure, the substance exists as a solid.
Now the normal melting and the normal boiling points, by definition are the temperatures at which the solid changes to liquid, and the liquid changes to gas at $1atm$ . So simply draw a horizontal line on the $y\;axis$ , and note the $x\; - intercepts$ of the transitions to give these properties.
The normal melting and boiling points are those when the pressure is $1atm$ . These can be found from the phase diagram by drawing a line across at $1{\text{ }}atmospheric{\text{ }}pressure$ . The phase diagram for water.

Note:
The boiling point diagram represents dynamic equilibrium of mole fraction of vapour and liquid phase at certain temperature at constant pressure. Boiling point diagram at constant pressure for binary mixture having component A and B is as below.