Calculate the average C-C bond strength in cyclopropane (in kJ/mol). Its combust

Question

Calculate the average C-C bond strength in cyclopropane (in kJ/mol). Its combustion and the experimental enthalpy of reaction are: C_3H_6(g) + 4.5O_2(g) right arrow 3CO_2(g) + 3H_20(g)delta H^o_rxn = -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). Answer -653

Explanation / Answer

The chemical reaction of combustion of C3H6 is as follows:

C3H6 + 4.5O2 ---> 3CO2 + 3H2O dH reaction = -1957.7 kJ/mol

Bond energy for C-H = 435 kj/ mol, O=O =496 KJ/ mol

6 x C-H =2610

4.5 x O=O = 2232

3 * C-C Bond = 3 x

Total energy = x+4842 kJ/mol this is endothermic reaction.

Bonds formed
6 x C=O = 4794
6 x H-O = 2784

Total energy = 7578 kJ/mol this is exothermic reaction.


Overall enthalpy change (3x+4842) + (-7578) = -1957.7 /mol

3X+4842 = 5620.3

3X = 778.3

X = 259.4 KJ/ mol

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