Question

A sample of water at 100°C is converted to steam after absorbing 820 kJ of heat. How grams of H2O are contained in the sample? Assume that the molar heat of vaporization of water is 41 kJ/mol.

Answer 1

Since water is already at 100°C all the energy is used to evaporate it.
Now we can calculate how many mols of water are evaporated with 820kJ.

`N= (820)/(41) =20 mol`
We calculated that we got 20 mols of water evaporated. Now, all we have to do is find how many grams is a mol of water. Molar mass of water is 20.16 g/mol.
The final answer is:

`m=20*20.16=403.2g`