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.