Vaporisation of Water at different altitudes

[Dean Lovett]

Hey All,

I am undertaking an experiment for a final report for a physics course at university. I have chosen to study the boiling point of water at a range of different pressures as a result of different altitudes.

I am using the Clausius-Clapeyron relation after obtaining the boiling point at a particular pressure to determine the vaporisation of water at that pressure. However, After taking the boiling point from 5 different altitudes (163m - 1065m above sea level) it appears that when i plug it all into the Clausius-Clapeyron relation the value for (delta)H_vap increases as the pressure decreases - Insinuating that more energy is required to vaporise the water at decreasing pressures.

I was under the impression that as the pressure decreases, the boiling point of the water decreases and as such so does the energy of vaporisation of water. I have managed to find a website that stands to support what i have found. However, The increase in energy at different altitudes confuses me.

I was wondering if someone would be able to help me out by point me towards a particular website/journal article in which i may be able begin to understand the phenomena.

Thank you in advance,
My best,
Dean.

 

[Simon Bridge]

It's something that gets covered in standard references - try your college library.
For your practical, you could just measure boiling points, specific heat, and latent heat, as you have no doubt seen in laboratories.
Just reproduce the standard experiments at different altitudes. The key to these things is usually to keep it simple - unless this is a post-grad exercise, you will usually be marked for your experimental technique/approach rather than being technically accurate or sophisticated.

As for resources - any casual google will get you pretty much what you need.