The heat of formation of octane is -251.1 kJ/mol.
To answer this question, we must first write the balanced reaction equation for octane combustion:
C₈H₁₈(l) + 12.5 O₂(g) → 8 CO₂(g) + 9 H₂O(g)
Now we use the formula for calculating the enthalpy of the reaction (ΔrH):
ΔrH = ∑ΔfH(products) - ∑ΔfH(reactants)
ΔrH(octane combustion) = 8 * ΔfH(CO₂) + 9 * ΔfH(H₂O) - 12.5 * ΔfH(O₂) - ΔfH(octane)
ΔfH - the heat of formation
ΔrH = -5074 kJ/mol
ΔfH for oxygen is 0 (as is for all elements)
ΔfH for carbon dioxide is -393.5 kJ/mol
ΔfH for water vapor is -241.8 kJ/mol
When we plug these values in the equation for ΔrH, we get:
-5074 kJ/mol = 8 * (-393.5 kJ/mol) + 9 * (-241.9 kJ/mol) - ΔfH(octane)
-5074 kJ/mol = -5325.1 kJ/mol - ΔfH(octane)
ΔfH(octane) = -5325.1 kJ/mol + 5074 kJ/mol
ΔfH(octane) = -251.1 kJ/mol
You can learn more about the heat of formation here:
brainly.com/question/13096727
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