Why does melting point of a substance decreases and boiling point of the substance increases ????
Why does melting point of a substance decreases and boiling point of the substance increases ????
Every liquid has what is called vapor pressure. Basically, few molecules of the liquid go into the gaseous phase and few from the gaseous phase turn back into liquid, this exists in an equilibrium condition (because, randomness!!). Now the pressure this gaseous phase of the liquid exerts over the surface the liquid is called as vapor pressure.
Boiling point is defined as the temperature at which vapor pressure is equal to the atmospheric pressure.
When we increase or decrease the surrounding pressure, vapor pressure also increases/decreases respectively.
So, when we increase the surrounding pressure, vapor pressure increases, and hence there is a lesser gap between the vapor pressure and the atmospheric pressure (note that atmospheric pressure remains constant). So, vapor pressure can be equal to the surrounding pressure at a lesser temperature.
Hence, on increasing the pressure, boiling point decreases and vice versa.
About melting point, as we increase pressure, the melting point increases. This is because, due to the increased pressure, it is easier for molecules to remain in solid form (this is what the whole liquefying a gas works on).
The stronger an intermolecular force, the higher the boiling point of the substance will be.
This is because stronger intermolecular bonds require more energy to break. As this energy is supplied in the form of heat when boiling, substances with stronger bonds will have a higher boiling point.
Every liquid has what is called vapor pressure. Basically, few molecules of the liquid go into the gaseous phase and few from the gaseous phase turn back into liquid, this exists in an equilibrium condition (because, randomness!!). Now the pressure this gaseous phase of the liquid exerts over the surface the liquid is called as vapor pressure.
Boiling point is defined as the temperature at which vapor pressure is equal to the atmospheric pressure.
When we increase or decrease the surrounding pressure, vapor pressure also increases/decreases respectively.
So, when we increase the surrounding pressure, vapor pressure increases, and hence there is a lesser gap between the vapor pressure and the atmospheric pressure (note that atmospheric pressure remains constant). So, vapor pressure can be equal to the surrounding pressure at a lesser temperature.
Hence, on increasing the pressure, boiling point decreases and vice versa.
About melting point, as we increase pressure, the melting point increases. This is because, due to the increased pressure, it is easier for molecules to remain in solid form (this is what the whole liquefying a gas works on).
The stronger an intermolecular force, the higher the boiling point of the substance will be.
This is because stronger intermolecular bonds require more energy to break. As this energy is supplied in the form of heat when boiling, substances with stronger bonds will have a higher boiling point.
