Final answer:
To calculate the enthalpy of combustion of ethanol, balance the chemical equation for combustion, use the given enthalpies of formation, sum for the products, subtract the reactants, and find the total change in enthalpy, which is -1368 kJ/mol, indicating an exothermic reaction.
Step-by-step explanation:
Calculating the Enthalpy of Combustion for Ethanol
The heat of combustion of a compound is the heat released when one mole of the substance is completely combusted in oxygen, forming water and carbon dioxide. To calculate the enthalpy of combustion of ethanol (C₂H₅OH), we first need to write the balanced chemical equation for its combustion:
C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l)
Next, we can use the enthalpies of formation to calculate the change in enthalpy:
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- Calculate the total enthalpy of the products (enthalpies of formation):
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- 2 mol CO₂(g) x (-394 kJ/mol) = -788 kJ
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- 3 mol H₂O(l) x (-286 kJ/mol) = -858 kJ
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- Total for products = -788 kJ + -858 kJ = -1646 kJ
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Subtract the enthalpy of the reactants from the products:
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- 1 mol C₂H₅OH(l) x (-278 kJ/mol) = -278 kJ
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- Total for reactants = -278 kJ
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Change in enthalpy (ΔH) = total products - total reactants = -1646 kJ - (-278 kJ) = -1368 kJ
The enthalpy of combustion of ethanol is therefore -1368 kJ/mol.
The calculated enthalpy indicates an exothermic reaction, where heat is released as ethanol combusts.
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