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In my textbook, a statement is given, as follows:

Boiling point of a liquid increases with increase in temperature

However, I was wondering, isn't this wrong? The boiling point of a liquid always remains the same, it doesn't change.

Hence, my question is: Is the above statement wrong? If it is, then under what conditions does the boiling point of a liquid change?

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3 Answers 3

up vote 4 down vote accepted

It sounds that they actually meant:

Boiling point of a liquid increases with increase in temperature pressure.

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Thanks for clarifying :) One thing more, can you please point me to an explanation (or give an explanation) of why does this happen ? – Gaurang Tandon Mar 30 '14 at 13:14
@GaurangTandon Think about it like this: if you have liquid under atmospheric pressure, it takes quite a bit of energy to get that liquid to excite and turn to gas. However, if it was 2x atmospheric pressure, it would take a lot more energy to excite the molecules in the liquid because there are more molecules pushing down on the liquid. – Jeremy Mar 30 '14 at 18:04

Given a pot of boiling water at one atmosphere pressure: Turn up the temperature of the burner. More heat (energy) is transferred to the pot down the temperature gradient as the water continues to boil at 100 C. Latent enthalpy of phase transition of one gram of water at 100 C to one gram of steam at 100 C is 540 cal/g. Faster heat input means faster rate of boiling.

Note that a 100 C boiling point only obtains at the surface. The bottom of the pot has hydrostatic head and therefore a higher boiling point. Sufficiently high temp at the bottom will get that boiling, too, resulting in faster heat transfer than mere convection. Too high a temp will obtain the Leidenfrost effect, suddenly dropping heat transfer to near zero. This is a tremendous problem in heat exchangers.
Leidenfrost temperature versus liquid, surface, and surface composition.

The world in non-linear. Do not believe engineers who think a line behaves as it travels to the right. Oil storage tank fires fought with water accumulate heating water at the tank bottom, under the hydrostatic head of the tank. The water superheats util it pushes the oil above it away, then it flashes to steam, expanding a thousand-fold, removing more hydrostatic head...resulting in a BLEVE. The expanding cloud of oil mist and steam, if ignited, is a fuel-air explosion. People get infrared thermal burns hundreds of meters distant.

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Your answer's a bit difficult to follow, thanks though. – Gaurang Tandon Mar 31 '14 at 4:52

I agree with @Klaus Warzecha's answer but I would like to add a little more to it.

They probably mean to say

Boiling point of a liquid increases with increase in pressure.

Since a liquid vaporises when molecules moves faster and farther apart but while increasing pressure, you are applying an external force o hold molecules closer to each other. Hence, molecules will require more energy to overcome this resistance thus this increases boiling point of liquid..!!


Boiling point of a liquid may also increase with decrease in volume of container.

I think there is no need to explain this further.

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Thanks for the help :) – Gaurang Tandon Mar 31 '14 at 4:52

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