Calculate the energy change of a full substance over temp range

Question

The following information is given for mercury at 1 atm:

boiling point = 356.6 °C		Hvap(356.6 °C) = 295.6 J/g
melting point = -38.90 °C	Hfus(-38.90 °C) = 11.60 J/g
specific heat gas = 0.1040 J/g °C	specific heat liquid = 0.1390 J/g °C

A 27.30 g sample of liquid mercury is initially at 267.70 °C. If the sample is heated at constant pressure (P = 1 atm), calculate the amount of energy in kJ needed to raise the temperature of the sample to 370.10 °C.

Answer 1

Here are the steps we need to go through:

1) liquid Hg @ 267.70º heated to boiling at 356.6º

2) phase change from liquid to gas @ 356.6º

3) heat the gas from 356.6º to 370.10º

Step 1:

q = mC∆T = (27.30 g)(0.1390 J/gº)(356.6 - 267.70) = 337.34 J

Step 2:

q = m∆Hvap = (27.30 g)(295.6 J/g) = 8069.9 J

Step 3:

q = mC∆T = (27.30 g)(0.1040 J/gº)(370.10 - 356.6) = 38.33 J

Add up all the joules:

337.34 + 8069.9 + 38.33

q = 8446 J x 1 kJ/1000 J = 8.446 kJ