Calculate the enthalpy of the reaction 2NO(g) + O2(g) rightarrow 2NO2(g) given t

Question

Calculate the enthalpy of the reaction 2NO(g) + O2(g) rightarrow 2NO2(g) given the following reactions and enthalpies of formation: 1/2N2(g) + O2(g) rightarrow NO2(g), Delta H degree = 33.2 kj 1/2N2(g) + 1/2O2(g) rightarrow NO(g), Delta H degree = 90.2 kJ Express your answer with the appropriate units. Calculate the enthalpy of the reaction 4B(s) + 3O2(g) rightarrow 2B2O3(s) given the following pertinent information: B2O3(s) + 3H2O(g) rightarrow 3O2(g) + B2H6(g), Delta H degree A = + 2035 kJ 2B(s) + 3H2(g) rightarrow B2H6(g), Delta H degree B = +36 kJ H2(g) + 1/2O2(g) rightarrow H2O(l), Delta H degree C = -285 kJ H2O(l) rightarrow H2O(g), Delta H degree D = +44 kJ

Explanation / Answer

Part A)

the enthalpy change for this reaction can be obtained as

H(rxn) = 2(HoA - HoB)

put the values of HoA and HoB

H(rxn) = 2(33.2-90.2) = -114 KJ

Part B)

The desired final reaction can be obtained by

the mathematical operation : 2B - 2A - 6C - 6D

so the desired enthalpy change will be obtained by Hess's law by the following expression

H(rxn) = 2(HB - HA) - 6(HC + HD)

= 2(36-2035) - 6(-285+44) = -3998 + 1446 = -2552 KJ

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