# A sample of H_2O with a mass of 46.0 grams has a temperature of 100°C. How many joules of energy are necessary to boil the water?

If you said $\Delta = 2.09 \cdot J \cdot {g}^{-} 1 \times 46.0 \cdot g$ you would be wrong.
The heat of vaporization of water, $\Delta {H}_{\text{vap}} \cong 2.26 \cdot k J \cdot {g}^{-} 1$. Your heat of vaporization is out by three order of magnitude, This is all too easy to do of course.