Question

NaCl has a (delta)Hfus = 30.2 kJ/mol and a (delta)Hvap = 171 kJ/mol. What mass of NaCl releases 452 kJ of heat as it changes into a gas? Use q=n(delta)H

2.64 g
22.1 g
155 g
875 g

Answer 1

The equation that is necessary in order to solve this item, is already written in the question as,
q = n(delta)H

However it was not defined which among the given heat constants is to be used. The situation given in this item is the changing of the phase from liquid to gas. Therefore, this involves the heat of vaporization (delta)Hvap.

The amount of NaCl is calculated through the equation,
n = q/ (delta Hvap)

Substituting the known values,
n = (452 kJ) / (171 kJ/mol)
n = 2.64 mol

Then, we multiply the obtained value by the molar mass of NaCl, 58.44 g/mol.

m = (2.64 mol)(58.44 g/mol)
m = 154.28 g

ANSWER: 154.28 g