When it comes to physical changes like phase changes, there are two types of heat energy: sensible heat and latent heat. Sensible heat is the heat absorbed/released when you heat the substance but it doesn't change phase. An example would be heating lukewarm water. The substance is liquid all throughout. Latent heat, on the other hand, is the heat absorbed/released when there is a phase change. An example would be boiling water, because it changes liquid to vapor.
Hence, for freezing liquid, you use the latent heat, specifically the heat of fusion. The answer should be
2.5 g * (1 mol/18.02 g) * 6.03 kJ/mol = 0.84 kJ/mol
The answer is not in the choices. You only use Hvap if you boil water.
First find the molar mass of Fe2O3, after you would want to do this
120 g Fe2O3 x 1 mol = # mol
Molar Mass
(solid)ice, because the molecules are very close together ,so they can keep the shape.
Answer: -
Mass of Hydrated KAl(SO₄)₂ = 2.0 g
Molar mass of anhydrous KAl(SO₄)₂ = 258.20 g/ mol
Mass of of anhydrous KAl(SO₄)₂ = mass of the 2nd heating = A
The mass of water released = mass of the Aluminum Cup + 2.0 grams of KAl(SO₄)₂ - mass of the 2nd heating
= H g
Moles of water released = 
Moles of anhydrous KAl(SO₄)₂ = 
Required ratio = 
