Question

How much energy (heat) is required to convert 248 g of water from 0oC to 154oC? Assume that the water begins as a liquid, that the specific heat of water is 4.184 J/g.oC over the entire liquid range, that the specific heat of steam is 1.99 J/g.oC, and the heat of vaporization of water is 40.79 kJ/mol.

Answer 1

q1 = heat needed to raise T from zero C to 100 C for the liquid.
q1 = mass H2O x specific heat x (Tfinal-Tinitial).

q2 = heat needed to vaporize liquid water at 100 C to steam at 100 C.
q2 = mass H2O x heat vap

q3 = heat needed to raise steam from 100 C to 154 C.
q3 = mass steam x specific heat x (Tfinal-Tinitial)
Then sum q1 + q2 + q3.
Note: Be VERY careful with the units. The problem quotes different units for the specific heat. You need to use the same unit which means converting them to the same, whichever you wish. The choice may be dictated by the units you have for mass H2O; i.e., you have grams, you might need to convert that to moles if you choose to use kJ/mol for sp. h.

Answer 2

I don't get it