Calculate the number of calories released when 20.0 g of steam condenses at 100.° C, cools to 0.0°C, and then freezes.

Question

(Hint: this calculation requires three steps.)

Answer 1

The 3 steps are...

1). heat released when 20.0 g of steam @ 100º condenses to liquid at 100º (phase change)

2). heat released when 20.0 g of liquid water cools from 100º to 0º

3). heat released when 20.0 g of liquid water at 0º freezes at 0º (phases change)

Calculations:

step 1). q = m∆Hvap = (20.0 g)(540 cal / g) = 10,803 cal

step 2). q = mC∆T = (20.0 g)(1 cal / gº)(100º) = 2,000

step 3. q = m∆Hfus = (20.0 g)(79.8 cal / g) = 1596 cal

TOTAL calories = 10,803 + 2,000 + 1596 = 14,399 calories