Chemistry - Thermochemistry Question with Solution | TestHub
When 0.1 mole of C8H18(l) at 300 K is completely burned at constant pressure in some oxygen gas at 300 K, yielding products gaseous H2O, CO and CO2 at 800 K, the process yielding 87.3 kcal of heat to the surrounding. Given:
Δf H (kcal/mol): C8H18(l) = -74.0, CO2(g) = -94.0, CO(g) = -26.5, H2O(g) = -58.0
Molar heat capacity at constant pressure (cal/K-mol): CO(g) = 7.0, CO2(g) = 8.0, H2O(g) = 6.0
Assume that all Δr H are independent of temperature.
The value of Δc H of C8H18(l) is (in kcal/mol)
Options:
Answer:
Solution:
The combustion of liquid octane is represented by the following reaction:
C8H18(l) + 25/2O2(g) tarrow 8CO2(g) + 9H2O(g)
The change in enthalpy of combustion, Δc H, is calculated as:
Δc H = 8(-94.0) + 9(-58.0) - (-74.0)
Δc H = -752 - 522 + 74
Δc H = -1200 kcal/mol
This corresponds to option (c).
