Question

Calculate the energy that must be removed to convert substance X from a gas at 116°C to a solid -44.6°C. Assume X has a molar mass of 75.0 g/mol.


ÄHvap 20. kJ/mol
C(s) 3.0 J/g·°C
ÄHfus 5.0 kJ/mol
C(l) 2.5 J/g·°C
bp 75°C
C(g) 1.0 J/g·°C
mp -15°C


please help! what formulas do i use?

Answer 1

For change of phase (example of vapor to liquid or liquid to a solid) use
q = mass x heat vaporization.
For the change in q with a single phase, (vapor or liquid or solid),
q = mass x specific heat x (delta T).
Then you add all of them together.

BUT, I don't think you can work this problem until you know how many grams (or how many mols) of substance X you have.