Use the table to answer the question.

Question

Reaction Bonds Present Energy of Bonds Broken and Formed (kJ/mol)
C + O2→CO2
O=O

2 C=O

499

1478

N2+O2→2NO
N≡N

O=O

2 N=O

946

499

1214

S+O2→SO2
O=O

2 S=O

499

1044

2CO+O2→2CO2
2 C≡O

O=O

4 C=O

2148

499

2956

Which reaction is endothermic?

(1 point)
Responses

N2+O2→2NO
N sub 2 plus O sub 2 rightarrow 2 N O

S+O2→SO2
S plus O sub 2 rightarrow S O sub 2

C + O2→CO2
C plus O sub 2 rightarrow C O sub 2

2CO+O2→2CO2

Answer 1

To determine which reaction is endothermic, we need to compare the total energy required to break the bonds with the total energy released when forming the bonds.

The general formula is: Total Energy of Bonds Broken - Total Energy of Bonds Formed = Change in Energy (ΔE)

If ΔE is positive, the reaction is endothermic.

Let's analyze each reaction:

1. C + O2 → CO2

   • Bonds broken: 1 O=O (499 kJ/mol)
   • Bonds formed: 2 C=O (2 × 799 kJ/mol = 1598 kJ/mol)
   • ΔE = 499 - 1598 = -1099 kJ/mol (exothermic)

2. N2 + O2 → 2NO

   • Bonds broken: 1 N≡N (946 kJ/mol) + 1 O=O (499 kJ/mol) = 1445 kJ/mol
   • Bonds formed: 2 N=O (2 × 607 kJ/mol = 1214 kJ/mol)
   • ΔE = 1445 - 1214 = 231 kJ/mol (endothermic)

3. S + O2 → SO2

   • Bonds broken: 1 O=O (499 kJ/mol)
   • Bonds formed: 2 S=O (2 × 522 kJ/mol = 1044 kJ/mol)
   • ΔE = 499 - 1044 = -545 kJ/mol (exothermic)

4. 2CO + O2 → 2CO2

   • Bonds broken: 2 C≡O (2 × 1072 kJ/mol = 2144 kJ/mol) + 1 O=O (499 kJ/mol) = 2643 kJ/mol
   • Bonds formed: 4 C=O (4 × 799 kJ/mol = 3196 kJ/mol)
   • ΔE = 2643 - 3196 = -553 kJ/mol (exothermic)

From this analysis, the reaction that is endothermic is:

N2 + O2 → 2NO