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In chemical reactions, heat is converted into chemical energy(the potential energy stored in chemical bonds) or vice versa. Bondenergy is the energy required to break one mole of the bond in thegas phase. Since it takes energy to break a bond, bond energies arealways positive. Conversely, energy is released when bonds areformed. Thus, the enthalpy change for a reaction can beapproximated from ΔHrxn=∑(ΔHbreaking)+∑(ΔHforming) where Hrepresents bond energies for the breaking (positive bond energy) orforming (negative bond energy) of a bond and Hrxn represents theoverall enthalpy for the reaction. Use the table to answerquestions about bond energies. Bond Bond energy (kJ/mol )

C−C 347

C=C 611

C−H 414

C−O 360

C=OinCO2 799

O−O 142

O=O 498

H−O 464

Calculate the bond energy per mole for breaking all the bonds inmethane, CH4. Express your answer to four significant figures andinclude the appropriate units.

Calculate the bond energy per mole for breaking all the bonds ofoxygen, O2? Express your answer to three significant figures andinclude the appropriate units.

Calculate the bond energy per mole for forming all the bonds ofwater molecules, H2O. Express your answer to three significantfigures and include the appropriate units.

Calculate the bond energy per mole for forming all the bonds ofcarbon dioxide, CO2. Express your answer to four significantfigures and include the appropriate units. ΔHCO2 =