Using heat of fusion

Question

Calculate the amount of heat needed to boil 70.1 g of methanol (CH3OH), beginning from a temp of -30.9°C.

Answer 1

For this problem, we have two steps. Step one is to find how much energy we need to raise the temperature from -30.9 C C to 64.6 C (boiling temp of methanol)

Q = mc * delta T

Q = 70.1 g * 2.53 J/g*C * (64.6 C - (-30.9 C)

Q = 16,937 J

To boil methanol, we need to use heat of vaporization which is 35.21 kJ/mol

molar mass of methanol is 32.04 g/mol

moles of methanol = 70.1 g / 32.04 g/mol = 2.19 mol

Q = moles of methanol * heat of vaporization

Q = 2.19 mol * 35.21 kJ/mol

Q = 77.11 kJ

Total heat required will be 16,937 J (16.937 kJ) added to 77.11 kJ, which is 94.05 kJ