Sorry for the late response but for this question, the answer is 3 moles of water.
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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.
<u>Answer:</u> The formation of given amount of oxygen gas results in the absorption of 713 kJ of heat.
<u>Explanation:</u>
To calculate the number of moles, we use the equation:
Given mass of oxygen gas = 83 g
Molar mass of oxygen gas = 32 g/mol
Putting values in above equation, we get:
For the given chemical equation:
<u>Sign convention of heat:</u>
When heat is absorbed, the sign of heat is taken to be positive and when heat is released, the sign of heat is taken to be negative.
By Stoichiometry of the reaction:
When 3 moles of oxygen gas is formed, the amount of heat absorbed is 824.2 kJ
So, when 2.594 moles of oxygen gas is formed, the amount of heat absorbed will be = 
Hence, the formation of given amount of oxygen gas results in the absorption of 713 kJ of heat.
