Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
Water boils at at , and its enthalpy of vaporisation is . Treat the enthalpy as constant. (a) The valve of a pressure cooker opens at an absolute pressure of . At what temperature does the water boil inside? (b) What is the vapour pressure of water at ? (c) At a camp the air pressure is . At what temperature does water boil there?
A liquid boils when its vapour pressure equals the outside pressure. The Clausius-Clapeyron equation is , with in kelvin and in J/mol. The vapour pressure does not depend on the amount of liquid or the size of the vessel.
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. at , and .
Step 1. The cooker. We want at , so . Then .
Step 2. The vapour pressure at . . . So .
Step 3. The camp. , so .
Check. A higher pressure gives a higher boiling point, and a lower pressure a lower one. Both agree with the direction of the changes.
Answer: in the cooker, at , and at the camp.
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