Using the values from the Appendix in your text, calculate the enthalpy of reaction H°rxn for the following reactions:

 

a. N2O4(g) + 4 H2→ N2(g) + 4 H2O (g)

 

b. 3 NO2(g) + H2O(l) → 2 HNO3(aq) + NO(g)

 

c. Cr2O3(s) + 3 CO(g) → 2 Cr(s) + 3 CO2(g)

 

(a.) Balanced equation : N₂O₄ (g) + 4 H₂ (g) ---> N₂ (g) + 4 H₂O (g)

Enthalpy of reaction, ?Δ?H^o_rxn = ?Δ?H^o_f products - ?Δ?H^o_f reactants

?Δ?H^o_rxn = [?Δ?H^o_f N₂ (g) + 4 * ?Δ?H^o_f H₂O (g)] - [?Δ?H^o_f N₂O₄ (g) + 4 * ?Δ?H^o_f H₂ (g)]

?Δ?H^o_rxn = [(0) + 4 * (-241.8 kJ/mol)] - [(9.2 kJ/mol) + 4 * (0)

?Δ?H^o_rxn = -967.2 kJ - 9.2 kJ

?Δ?H^o_rxn = -976.4 kJ

(b.) Balanced equation : 3 NO₂ (g) + H₂O (l) ---> 2 HNO₃ (aq) + NO (g)

Enthalpy of reaction, ?Δ?H^o_rxn = ?Δ?H^o_f products - ?Δ?H^o_f reactants

?Δ?H^o_rxn = [2 * ?Δ?H^o_f HNO₃ (aq) + ?Δ?H^o_f NO (g)] - [3 * ?Δ?H^o_f NO₂ (g) + ?Δ?H^o_f H₂O (l)]

?Δ?H^o_rxn = [2 * (-207.4 kJ/mol) + (90.3 kJ/mol)] - [3 * (33.2 kJ/mol) + (-285.8 kJ/mol)]

?Δ?H^o_rxn = -414.8 kJ + 90.3 kJ - 99.6 kJ + 285.8 kJ

?Δ?H^o_rxn = -138.3 kJ

(c) Balanced equation : Cr₂O₃ (s) + 3 CO (g) ---> 2 Cr (s) + 3 CO₂ (g)

Enthalpy of reaction, ?Δ?H^o_rxn = ?Δ?H^o_f products - ?Δ?H^o_f reactants

?Δ?H^o_rxn = [2 * ?Δ?H^o_f Cr (s) + 3 * ?Δ?H^o_f CO₂ (g)] - [?Δ?H^o_f Cr₂O₃ (s) + 3 * ?Δ?H^o_f CO (g)]

?Δ?H^o_rxn = [2 * (0) + 3 * (-393.5 kJ/mol)] - [(-1139.7 kJ/mol) + 3 * (-110.5 kJ/mol)]

?Δ?H^o_rxn = -1180.5 kJ + 1139.7 kJ + 331.5 kJ

?Δ?H^o_rxn = 290.7 kJ