Chemistry 2720 Fall 1999 Quiz 3 solution

From the enthalpy of vaporization at the boiling point, we can compute the enthalpy of vaporization at . The following diagram traces out the path to be used for this computation:

We compute the enthalpy changes in steps 1, 2 and 3 and add them to get the enthalpy of vaporization at the standard temperature:

However, . Therefore

The accepted value (in case you're curious) is . The above calculation, which doesn't take into account the variation of heat capacity with temperature, gives a very good result.