Given ΔHf(CO 2 ) = −393.5, ΔHf(H 2 O, l) = −285.8 and ΔHf(C 2 H 5 OH, l) = −277.0 kJ/mol, the standard enthalpy of combustion of ethanol is:

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Given ΔHf(CO2) = −393.5, ΔHf(H2O, l) = −285.8 and ΔHf(C2H5OH, l) = −277.0 kJ/mol, the standard enthalpy of combustion of ethanol is:

Answer: −1367 kJ/mol.

A −1367 kJ/mol
B −1644 kJ/mol
C −1090 kJ/mol
D −2734 kJ/mol

Correct answer: A. −1367 kJ/mol

Explanation: C2H5OH + 3O2 → 2CO2 + 3H2O: ΔH = [2(−393.5) + 3(−285.8)] − (−277.0) = −1644.4 + 277 = −1367 kJ/mol.

Isothermal expansion follows a gentler curve (heat flows in to keep T constant) while adiabatic expansion drops in pressure more steeply (no heat exchange, so internal energy and temperature fall as the gas does work).

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Study energy changes in chemical reactions. Understand enthalpy, entropy, Gibbs free energy, and the laws of thermodynamics that decide whether a reaction will occur spontaneously or not.

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Given ΔHf(CO<sub>2</sub>) = −393.5, ΔHf(H<sub>2</sub>O, l) = −285.8 and ΔHf(C<sub>2</sub>H<sub>5</sub>OH, l) = −277.0 kJ/mol, the standard enthalpy of combustion of ethanol is:

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