To determine which reaction is endothermic, we need to compare the energy of the bonds broken and formed for each reaction. An endothermic reaction occurs when the energy required to break the bonds (reactants) is greater than the energy released during the formation of new bonds (products).
Let's calculate the total energy for each reaction.
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C + O2 → CO2
- Bonds broken: 1 O=O (499 kJ/mol)
- Bonds formed: 2 C=O (2 × 799 kJ/mol = 1598 kJ/mol)
- Total: 499 kJ (bonds broken) - 1598 kJ (bonds formed) = -1099 kJ (exothermic)
-
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 × 1214 kJ/mol = 2428 kJ/mol)
- Total: 1445 kJ (bonds broken) - 2428 kJ (bonds formed) = -983 kJ (exothermic)
-
S + O2 → SO2
- Bonds broken: 1 O=O (499 kJ/mol)
- Bonds formed: 2 S=O (2 × 522 kJ/mol = 1044 kJ/mol)
- Total: 499 kJ (bonds broken) - 1044 kJ (bonds formed) = -545 kJ (exothermic)
-
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)
- Total: 2643 kJ (bonds broken) - 3196 kJ (bonds formed) = -553 kJ (exothermic)
Since all of the calculations yield negative values, this means that all reactions listed are actually exothermic rather than endothermic.
If there were an error or misunderstanding in the premise of something being clearly endothermic in the provided options, I would need additional information to identify a properly characterized endothermic reaction.
However, given what we have, none of the reactions in the provided list appears to be endothermic.