Question

Use the table to answer the question.

Bonds and Bond Energies for Given Reactions
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

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

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

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

Answer 1

To determine which reaction is endothermic, we need to look at the bond energies provided in the table. A reaction is considered endothermic if the total energy required to break the bonds in the reactants is greater than the total energy released from forming the bonds in the products.

We can calculate the energy changes for each reaction using the bond energies provided:

1. **C + O2 → CO2**
- Bonds broken: 1 O=O (499 kJ/mol)
- Bonds formed: 2 C=O (2 × 799 kJ/mol = 1598 kJ/mol)
- Energy change = Energy of bonds broken - Energy of bonds formed = 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)
- Energy change = 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)
- Energy change = 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)
- Energy change = 2643 - 3196 = -553 kJ/mol (exothermic)

Based on the calculations above, the only reaction that resulted in a positive energy change, indicating it is endothermic, is:

**N2 + O2 → 2NO**