# How do we know a substance is a solid, liquid  or gas by simply knowing its melting or boiling points?I'd appreciate if someone could just explain me the whole thing. Like if both the melting and...

How do we know a substance is a solid, liquid  or gas by simply knowing its melting or boiling points?

I'd appreciate if someone could just explain me the whole thing. Like if both the melting and boiling points are in the negative is the substance considered to be a solid, liquid or gas. Likewise if a  substance has a melting point of 0 and boiling point  108 or 110 is it a solid liquid or gas.

Expert Answers
jeew-m | Certified Educator

Melting point and boiling point are temperatures. The melting point and boiling point is dependant on pressure as well. Usually these temperatures are expressed related to the standard pressure of 1 atm and room temperature of 25C. Here onwards my explanations are based on standard pressure.

Melting Point

This is the temperature at which a solid become a liquid. When we increase the temperature of a solid it will become liquid at its melting point. At low temperatures than melting point the substance remain as a solid. Then from melting point temperature to boiling point the substance will remain as a liquid.

Boiling point

This is the temperature at which a liquid become a gas. When we increase the temperature of a liquid it will become gas at its boiling point. Boiling point is greater than melting point. After the boiling point the substance will remain as gas.

Now let us consider a substance where melting point is 50C and boiling point is 100C. So at room temperature or at 25C it will be a solid. Because its melting point is 50C.

Let us again consider a substance where melting point is 10C and boiling point is 50C. Not at room temperature it will be a liquid.

For a substance which is having melting point -20C and boiling point -5C at room temperature it will remain as a gas because room temperature is above boiling point.

For your example;

Melting point  = 0C

Boiling point  = 108C

At room temperature the substance is at a temperature between melting point and boiling point. So it Will be a liquid.

So the phase of a substance liquid gas or solid depends on their melting points, boiling points, room temperature and pressure.

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