Chemistry - Thermochemistry Question with Solution | TestHub
Only gases remains after 15.0 g of carbon is treated with 20 l of air at 380 K and 8.21 atm pressure. (Assume 19% by volume oxygen, 80% nitrogen, 1% carbon dioxide). Determine the amount of heat evolved (in kcal) under constant pressure. Enthalpies of formation of CO2(g) and CO(g) are -96.0 and -26.0 kcal/mol, respectively.
Answer:
Solution:
The moles of air are calculated as:
nair = (8.21 × 20)/(0.0821 × 380) = 5.263 mol
Thus, the moles of O₂ are:
nO2 = 0.19 × 5.263 = 1.0 mol
The moles of carbon are:
nC = 15.0/12 = 1.25 mol
Let x mol of carbon form CO₂ and y mol of carbon form CO. We can set up the following equations:
x + y = 1.25 (Carbon balance)
x + y/2 = 1.0 (Oxygen balance based on O2)
Solving these equations gives x = 0.75 and y = 0.5.
The total heat evolved is:
Heat evolved = (0.75 × 96) + (0.5 × 26) = 72 + 13 = 85 kcal
The answer is 0085.
