Chemistry - Thermochemistry Question with Solution | TestHub
The enthalpies of formation of FeO(s) and Fe2O3(s) are -65.0 and -197.0 kcal/mol, respectively. A mixture of the two oxides contains FeO and Fe2O3 in the mole ratio 2:1. If by oxidation it is changed in to a 1:2 mole ratio mixture, how much of thermal energy will be released per mole of the initial mixture?
Options:
Answer:
Solution:
Consider an initial mixture of 3 mol, consisting of 2 mol FeO and 1 mol Fe₂O₃. This mixture contains a total of 2 + 2 = 4 mol of Fe.
The final mixture contains x mol of FeO and 2x mol of Fe₂O₃. Since the amount of Fe remains constant, we can set up the equation: x + 4x = 4.
Solving for x, we get x = 0.8.
Thus, the final mixture contains 0.8 mol FeO and 1.6 mol Fe₂O₃.
The initial enthalpy, Hinitial, is calculated as:
Hinitial = 2(-65) + (-197) = -130 - 197 = -327 kcal
The final enthalpy, Hfinal, is calculated as:
Hfinal = 0.8(-65) + 1.6(-197) = -52 - 315.2 = -367.2 kcal
The heat released is the difference between the initial and final enthalpies:
Heat released = Hinitial - Hfinal = -327 - (-367.2) = 40.2 kcal
This heat is released per 3 mol of the initial mixture.
Therefore, the heat released per mole of the initial mixture is:
40.2 kcal/3 mol = 13.4 kcal/mol
This corresponds to option (a).
