018 Fall 2015 Bond Energies and Standard Enthalpy Change of the Reaction l react

Question

018 Fall 2015 Bond Energies and Standard Enthalpy Change of the Reaction l reactions, heat is converted into chemical e potential energy slored in chomical bonds) or Bond energy is the energy required to break of the bond in the gas phase. Energy is required onds. Conversely, energy is released when formed. Thus, the enthalpy change (AH) fora an be approximated tiom Calculate the bond energy for breaking all the bonds in a mole of methane, CHa Express your answer to four significant figures and include the appropriate units. energy required energy released kJ mo = . to break bonds forming bonds represents bond energies for the breaking ond energy) or forming (negative bond energy) of d Hn represents the overall enthalpy for the Ala4° | 1388 13mol Hints My. Answers Give Up Review Part Incorrect; Try Again; 4 attempts remaining; no points deducted You may have calcufated the amount of energy needed to break four moles of C- C bonds. CHs contains only C-H bonds able to answer questions about bond energies Bond energy Bond (kJ/mol) C-C 347 CC611 Part B Calculate the bond energy for breaking all the bonds in a mole of O2 molecules? Express your answer to three significant figures and include the appropriate units. 414 C- C-o C-O 736 0O142 O-O 498 H-O464 H 360 kJ mol ano, 1498 arch the web and Ww

Explanation / Answer

A) The bond energy of One C-H bond = 414KJ / mole

So bond energy for four C-H bonds = 4X 414 = 1656 KJ / mol

B) In O2 only one O=O bond is present

So bond energy = O=O bond energy = 498 KJ / mol

C) There are two O-H bonds in H2O

O2 + 2H2 --> 2H2O

so bond energy in formation of 2 moles of H2O = bond energy of reactants- bond energy of products

Bond energy = BE of O2 + 2X BE of H2 - 2BE (2XO-H)

Bond energy = 498 + 872.8 - 1856 = -485.2 KJ / mole

D) Bond energy for formation of CO2

Bond energy = bond energy of reactants - bond energy of products

C+ O2 --> CO2

Bond energy = Bond energy of O=O - 2X B.E. C=O = 498 - 1472 = -974 KJ / mol

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