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Calculate the enthalpy change (ΔH) for the reaction: 2NO(g) + O2(g) → 2NO2(g) gi

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Question: Calculate the enthalpy change (ΔH) for the reaction: 2NO(g) + O2(g) → 2NO2(g) given the following bond enthalpies: N≡N = 941 kJ/mol, O=O = 498 kJ/mol, N=O = 201 kJ/mol.

Options:

  1. -180 kJ
  2. -200 kJ
  3. -220 kJ
  4. -240 kJ

Correct Answer: -220 kJ

Solution: 

ΔH = [2(201) + 498] - [2(941)] = -220 kJ.

Calculate the enthalpy change (ΔH) for the reaction: 2NO(g) + O2(g) → 2NO2(g) gi

Practice Questions

Q1
Calculate the enthalpy change (ΔH) for the reaction: 2NO(g) + O2(g) → 2NO2(g) given the following bond enthalpies: N≡N = 941 kJ/mol, O=O = 498 kJ/mol, N=O = 201 kJ/mol.
  1. -180 kJ
  2. -200 kJ
  3. -220 kJ
  4. -240 kJ

Questions & Step-by-Step Solutions

Calculate the enthalpy change (ΔH) for the reaction: 2NO(g) + O2(g) → 2NO2(g) given the following bond enthalpies: N≡N = 941 kJ/mol, O=O = 498 kJ/mol, N=O = 201 kJ/mol.
  • Step 1: Identify the bonds broken and formed in the reaction. The reaction is 2NO(g) + O2(g) → 2NO2(g).
  • Step 2: For the reactants (2NO and O2), identify the bonds: Each NO has one N=O bond, and O2 has one O=O bond.
  • Step 3: Calculate the total bond enthalpy for the bonds broken: 2(N=O) + 1(O=O). Using the bond enthalpy values, this is 2(201 kJ/mol) + 498 kJ/mol.
  • Step 4: For the products (2NO2), identify the bonds: Each NO2 has two N=O bonds. So for 2NO2, there are 2(2 N=O) bonds.
  • Step 5: Calculate the total bond enthalpy for the bonds formed: 2(2 N=O) = 4(N=O). Using the bond enthalpy value, this is 4(201 kJ/mol).
  • Step 6: Now, calculate the total bond enthalpy for the bonds broken: 2(201) + 498 = 402 + 498 = 900 kJ.
  • Step 7: Calculate the total bond enthalpy for the bonds formed: 4(201) = 804 kJ.
  • Step 8: Use the formula ΔH = (Total bonds broken) - (Total bonds formed). So, ΔH = 900 kJ - 804 kJ.
  • Step 9: Calculate ΔH: 900 kJ - 804 kJ = 96 kJ.
  • Step 10: Since the reaction is exothermic, we take the negative value: ΔH = -96 kJ.
  • Bond Enthalpy Calculation – Understanding how to calculate the enthalpy change of a reaction using bond enthalpies.
  • Reaction Stoichiometry – Applying stoichiometric coefficients from the balanced chemical equation to bond enthalpy values.
  • Sign of Enthalpy Change – Recognizing that a negative ΔH indicates an exothermic reaction.
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