How do you calculate entropy of vaporization?

Question

Wyatt Atkins · Accepted Answer

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.

The formula for heat of vaporization is: calories gained by the substance increasing in temperature 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." To find heat in calories, multiply the mass of the object gaining or losing heat (grams) by its change in temperature (final temp - initial temp) by its specific heat (for water it is 1). Again, the mixed temperature at the end of the experiment will be the water in the thermos after all of the water in the test tube has evaporated. A typical setup 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 its initial temperature would be 100 degrees Celsius. The thermos water is gaining heat and its initial temperature will have to be measured before beginning the lab.

Caleb Adams · Answer

undefined The entropy of vaporization ($ \Delta S_{\text{vap}} $) is calculated using the equation:

$$ \Delta S_{\text{vap}} = \frac{\Delta H_{\text{vap}}}{T} $$

Where:
- $ \Delta S_{\text{vap}} $ is the entropy change during vaporization.
- $ \Delta H_{\text{vap}} $ is the enthalpy change during vaporization.
- $ T $ is the absolute temperature in Kelvin.

Wyatt Atkins · Answer

undefined The entropy of vaporization (ΔS_vap) can be calculated using the equation:

ΔS_vap = ΔH_vap / T

Where:
ΔS_vap = entropy of vaporization
ΔH_vap = enthalpy of vaporization
T = temperature in Kelvin