9.10 - Key: 10. Use the average bond enthalpies in BLBM...

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Key: 10. Use the average bond enthalpies in BLBM Table 8.4 to estimate the heat of formation of water. a. -486 kcal/mol b. -486 kJ/mol c. 486 kcal/mol d. 486 kJ/mol e. -243 kJ/mol f. 243 kJ/mol g. 168 kJ/mol h. -168 kJ/mol To answer this problem you need to understand what the heat of formation is, and how to use bond enthalpies to determine the enthalpy of a reaction. A heat of formation ( ΔH° f ) is the energy required to form one mole of a certain molecule from elements in their standard state. The reaction representing the heat of formation of water would be: 1H 2 + ½O 2 → 1H 2 O Now let’s go over bond enthalpies. Bond enthalpy is the energy required to break a bond. When a reaction takes place, it can be assumed that all of the bonds of the reactants are breaking and all of the bonds of the products are forming. To determine the overall enthalpy of the reaction, we must add up the energy required to break each bond of the reactants and subtract all of the energy released when the bonds in the products are formed. The bond enthalpy of the reactants is
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9.10 - Key: 10. Use the average bond enthalpies in BLBM...

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