Calculate the amount of heat required to vaporize 75 g of water at 75 Celsius

Answer 1

In order to properly answer this question, one needs to know the ∆Hvaporization for water, as well as the specific heat of water.

Looking up these values, I find the following:

Specific heat = C = 4.184 J/gº

∆Hvap = 2260 J/g

Step 1: heat needed to raise temperature of 75 g water from 75º to 100º

q = mC∆T = (75 g)(4.184 J/gº)(25º) = 7845 J

Step 2: heat needed to vaporize 75 g water at 100º

q = (m)(∆Hvap) = (75 g)(2260 J/g) = 169,500 J

Sum the heats to get

7845 J + 169,500 J = 177,345 J = 177 kJ = 180 kJ (2 sig. figs.)