Use the bond energies provided to estimate ? r H° for the reaction below. C 2 H 4 (g) + H 2 (g) ? C 2 H 6 (g) ? r H°= ?
Bond Bond Energy (kJ mol -1 )
C-C 347
C-H 414
C=C 611
C?C 837
H-H 436
A) -128 kJ mol -1
B) +98 kJ mol -1
C) +700 kJ mol -1
D) -102 kJ mol -1
E) -166 kJ mol -1

Question

Use the bond energies provided to estimate ? r H° for the reaction below. C 2 H 4 (g) + H 2 (g) ? C 2 H 6 (g) ? r H°= ?
Bond Bond Energy (kJ mol -1 )
C-C 347
C-H 414
C=C 611
C?C 837
H-H 436
A) -128 kJ mol -1 
B) +98 kJ mol -1 
C) +700 kJ mol -1 
D) -102 kJ mol -1 
E) -166 kJ mol -1

Quizplus · Accepted Answer

We can determine ΔS1U1B1rS1U1B0H°S1U1B1 using bond energies by calculating the total energy required to break the bonds in the reactants and the total energy released in the formation of bonds in the products.

Reactants:
- 1 C-C bond (347 kJ/mol) 
- 2 C-H bonds (2 x 414 kJ/mol)
- 1 S-H bond (436 kJ/mol)

Products:
- 1 C-C bond (347 kJ/mol)
- 2 C-H bonds (2 x 414 kJ/mol)
- 1 C-S bond (240 kJ/mol)
- 1 S-H bond (436 kJ/mol)

ΔS1U1B1rS1U1B0H°S1U1B1 = ∑(bonds broken) - ∑(bonds formed)
ΔS1U1B1rS1U1B0H°S1U1B1 = (1 x 347) + (2 x 414) + (1 x 436) - (1 x 347) - (2 x 414) - (1 x 240) - (1 x 436)
ΔS1U1B1rS1U1B0H°S1U1B1 = -128 kJ/mol

Therefore, the best choice is A, which represents a negative value for ΔS1U1B1rS1U1B0H°S1U1B1, indicating that the reaction releases energy (exothermic) and is more stable in terms of energy compared to the reactants.

Use the Bond Energies Provided to Estimate ?rH° for the Reaction

Use the Bond Energies Provided to Estimate ?_rH° for the Reaction