How do you calculate entropy of vaporization?

1 Answer
Aug 7, 2015


In order to calculate heat of vaporization you need to know how to calculate heat. Heat is measured in several units: Joules, Calories, and BTU.


To find heat in Calories, multiply the mass of the object gaining or losing heat (grams) by it's change in temperature (final temp - initial temp) by it's specific heat (for water it is 1 otherwise look up specific heat in book or internet).
Then the formula for heat of vaporization is:
Calories gained by the the substance increasing in temp. minus
Calories lost by the substance being vaporized divided by the mass of the substance being vaporized (grams). Use the mixed temperature as your "final temperature."

A typical set up for this is heating water in a test tube attached to a rubber hose that is going into a thermos of water. The test tube water is being vaporized and it's initial temperature would be 100 degrees Celsius. The thermos water is gaining heat and it's initial temperature will have to measured before beginning the lab. Again, the mixed temperature, after all of the water in the test tube is vaporized, will be the water in the thermos at the end of the experiment.