Using the table of average bond energies below,the ΔH for the reaction is ________ kJ. Bond: C≡C C-C H-I C-I C-H D (kJ/mol): 839 348 299 240 413
A)+160
B)-160
C)-217
D)-63
E)+63

Question

Using the table of average bond energies below,the ΔH for the reaction is ________ kJ.  Bond: C≡C C-C H-I C-I C-H D (kJ/mol): 839 348 299 240 413
A)+160 
B)-160 
C)-217 
D)-63 
E)+63

Quizplus · Accepted Answer

The bond dissociation energy (D) for HI is 299 kJ/mol, and that for H-Cl is 431 kJ/mol. Bond formation between I2 and Cl2 releases energy equal to the sum of the bond dissociation energies of H-I and Cl-Cl and the bond formation energy of I-Cl. 
ΔH = [2(D(Cl-Cl)) + D(H-I)] - D(I-Cl) 
ΔH = [2(431) + 299] - 240 = -217 kJ/mol
Therefore, the ΔH for the reaction is -217 kJ/mol. The best choice is C, which is the negative value closest to the calculated value.

Using the Table of Average Bond Energies Below,the ΔH for the Reaction