Heats of reaction calculated from bond energies and from heats of formation are

Question

Heats of reaction calculated from bond energies and from heats of formation are often, but not always, close to each other. a. Industrial ethanol (CH3CH2OH) is produced by a catalytic reaction of ethylene (CH2=CH2) with water at high pressures and temperatures. Calculate Hºrxn for this gas-phase hydration of ethylene to ethanol, using bond energies and then using heats of formation. b. Ethylene glycol is produced b the catalytic oxidation of ethylene to ethylene oxide, which then reacts with water to form ethylene glycol: image from custom entry tool + H2O (l) = HOCH2CH2OH(l) The Hºrxn for this hydrolysis step, based on heats of formation, is -97 kJ/mol. Calculate Hºrxn for the hydrolysis using bond energies.

Explanation / Answer

+ H2O (l) = HOCH2CH2OH(l) The Hºrxn

A. Don't forget to look up the enthalpy of formation of steam (gaseous water) and not liquiid water.
B. You break one C-O bond and one O-H bond, and you make one C-O bond and one O-H bond. Theoretically zero.

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