Question

At 25 degrees Celsius, 1 atm, 2.1 grams of iron powder combined with sulfur gives off 0.87 kcal (under isostatic conditions). The heat of decomposition of iron sulfide is:

A) 2.12kcal

B) 1.25kcal

C) 0.87kcal

D) 0.43kcal

Answer 1

The heat of decomposition of iron sulfide is the same as the heat released during its formation but with an opposite sign. Since 0.87 kcal is released when iron and sulfur combine, the decomposition would absorb 0.87 kcal making the correct answer 0.87 kcal.

Step-by-step explanation:

The question concerns the heat of decomposition of iron sulfide. When 2.1 grams of iron powder reacts with sulfur, it gives off 0.87 kcal of heat energy under isostatic conditions at 25 degrees Celsius and 1 atm pressure. Decomposition reactions are the reverse of combination reactions, so the heat of decomposition should be equal to the heat of combination but with an opposite sign.

Considering the principle of conservation of energy, the heat given off in the reverse reaction (decomposition) would be the same as the heat taken in during the formation reaction (combination). Therefore, the heat of decomposition of iron sulfide would be the same amount of energy released, 0.87 kcal, but it would be absorbed by the system, making the correct answer C) 0.87 kcal.