Question

Calculate the energy that must be removed to convert substance X from a gas at 115°C to a solid -50.7°C. Assume X has a molar mass of 75.0 g/mol.

Specific heat capacities
ΔHvap 20. kJ/mol C(s) 3.0 J/g · °C
ΔHfus 5.0 kJ/mol C(l) 2.5 J/g · °C
bp 75°C C(g) 1.0 J/g · °C
mp −15°C

If you can go step by step so I can understand how this is done That would be great! Thanks

Answer 1

You must know how many grams or how many moles you have initially. If moles, ok. If mass, convert mass to moles.
q1 = heat removed to move from 115 C to b.p.
q1 = mols x specific heat vapor x (Tfinal-Tinitial).

q2 = heat removed to convert vapor to liquid.
q2 = moles x heat vaporization.

q3 = heat removed to move from b.p. to melting point.
q3 = moles x specific heat liquid x (Tfinal - Tinitial).

q4 = heat removed to freeze liquid at m.p.
q4 = moles x heat fusion.

q5 = heat removed to move from m.p. to -50.7.
q5 = moles x specific heat solid x (Tfinal-Tinitial).

qtotal = q1+q2+q3+q4+q5