The standard molar enthalpy of vaporization for water is 40.79kJ/mol. What mass of steam is required to release 500 kJ of energy upon condensation?

220.9g of water are required

Explanation:

The molar enthalpy of vaporization is defined as the heat released when 1 mole of water changes from liquid to gas.

For water, 1 mole releases 40.79kJ. To release 500kJ are necessaries:

500kJ * (1mol / 40.79kJ) = 12.26 moles are necessaries

To convert moles to grams we must use the molar mass (H2O = 18.02g/mol):

12.26 moles * (18.02g / 1 mol) =

your answer would be a. 12.5 kg