The value of Δ r H for the reaction: C 8 H 18 (l) + 17/2O 2 (g) → 8CO(g) + 9H 2 O(g) is (in kcal/mol)

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ChemistryThermochemistryEnthalpy of CombustionMedium2 minQB

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Passage / Comprehension

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:

Δ_f 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 Δ_r H are independent of temperature.

The value of Δ_r H for the reaction:

C₈H₁₈(l) + 17/2O₂(g) → 8CO(g) + 9H₂O(g)

is (in kcal/mol)

Options:

Answer:

Solution:

The change in enthalpy, Δ_r H, is calculated as follows:

Δ_r H = 8(-26.5) + 9(-58.0) - (-74.0)

Δ_r H = -212 - 522 + 74

Δ_r H = -660 kcal/mol

This corresponds to option (d).

Stream:JEESubject:ChemistryTopic:ThermochemistrySubtopic:Enthalpy of Combustion

⏱ 2mℹ️ Source: QB

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