Calculating a Heat of Reaction

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Background

Consider the following example:

2 H₂ +  O₂ --->  2 H₂O  Q = ?

When a sample of H₂ with a mass of 1.25 grams is burned in a bomb calorimeter, 42.8 kcal of heat is produced. The value for Q that should be associated with the above equation, however, is the quantity of heat that would have been produces by two moles of hydrogen (2 H₂). This value can be computed from the calorimeter data:

Q/M = Q'/M'  or  X/2 H₂ = 42.8 kcal/1.25 g  or  X/4.00 g = 42.8 kcal/1.25 g

X = 137 kcal

Textbook Discussion: Sections 7.10 & 7.11, pages 227-232. See Also: Example IX, X, and XI, pages 228, 229, and 230.

Problem

The following incomplete balanced thermochemical chemical equation represents the combustion of hydrogen sulfide(H₂S):

2 H₂S + 3 O₂ ---> 2 SO₂ + 2 H₂O     Q = - ? kcal

In this equation, all substances are at standard state conditions. Calorimetric data indicates that the complete combustion of 97.0 grams of hydrogen sulfide by this reaction releases 381 kilocalories. According to this data, what Q value should be used to complete the above themochemical equation? Atomic Masses: H=1.00 S=32.1 O=16.0 amu