Intense thermochemistry problem

m w's solution is just fine, there is no mistake. The fact that the final temperature is 22 C only serves to help us determine that the water changes 13 C (this is the reason for 35 minus 22). The division comes about as you do the algebra to solve for m.

In addition, Ian Tonner says:

"You might be wondering why I used .00418 instead of 4.18."

I would point out that m w's solution provides for consistency of units. If you look here:

(50g) x (2.4 kJ/g) x (1000J/1kJ)

you will see that the third term converts from kJ to J.

If you want to see problems of this ilk, I have several (maybe none of this exact type) here:

http://www.chemteam.info/Thermochem/Ther…

heat gained by water evaporating = heat lost by water cooling

m dHvap = m Cp dT
(50g) x (2.4 kJ/g) x (1000J/1kJ) = m x (4.184 J/g°C) x (35°C - 22°C)

solve for m