Chemistry - Thermochemistry Question with Solution | TestHub
Study the following thermochemical equations:
(a) N2O(g) + 3H2(g) → H2O(l) + N2H4(l); ΔH = -75.56 kcal
(b) 4N2(g) + 3H2O(l) → 2NH3(g) + 3N2O(g); ΔH = +241.35 kcal
(c) N2H4(l) + H2O(l) → 2NH3(g) + 1/2 O2(g); ΔH = +34.18 kcal
(d) H2O(l) → H2(g) + 1/2 O2(g); ΔH = +68.32 kcal
Ammonia can be obtained according to reaction (b) or (c). Which of the following is correct regarding these reactions, for the same mass of ammonia formed?
Options:
Answer:
Solution:
Both reactions yield 2 mol (34 g) of NH₃. For reaction (b), the mass of reactants is 4(28) + 3(18) = 166 g. For reaction (c), the mass of reactants is 32 + 18 = 50 g. Therefore, reaction (b) requires a greater mass of reactants, which makes options (a) and (b) false. The heat absorbed for reaction (b) is 241.35 kcal, while for reaction (c) it is 34.18 kcal. Thus, reaction (b) requires more heat. The correct answer is (c).
