Calculate the average C—C bond strength in cyclopropane (in kJ/mol). Its combust
ID: 1051388 • Letter: C
Question
Calculate the average C—C bond strength in cyclopropane (in kJ/mol). Its combustion and the experimental enthalpy of reaction are: C3H6(g) + 4.5O2(g) 3CO2(g) + 3H2O(g) Hºrxn = -1,957.7 kJ/mol Since all reactants and products are in the gaseous state, bond energies may be used to estimate the enthalpy of reaction. Do not use the standard C—C bond strength, leave the C—C bond strength as an unknown and solve for its value. For review see chapter 9 p. 392 (Tro) or chapter 13 p. 608 (Zumdahl).
Average Bond Energies (kJ/mol)
O-H 463
O=O 498
C-H 414
C=O 745
C-C 347
C=O (CO2 799)
Explanation / Answer
on reactant side:
2 : C-C bond
6: C-H bond
4.5 : O=O bond
on product side:
6 : C=O bond
6 : O-H bond
delta H = BE (reactant) - BE (product)
-1957.7 = 2*(C-C) + 6*(414) + 4.5*(498) - 6*(745) -6*(463)
2(C-C) = 565.3
C-C = 282.65 KJ/mol
Answer: 282.65 KJ/mol
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