To find the enthalpy change for the reaction NO + 3/2H2O - NH3 + 5/2O2 using the given reaction 4NH3 + 5O2 - 4NO + 6H2O, you need to apply the concept of Hess's Law.
Hess's Law states that the total enthalpy change for a reaction is independent of the pathway taken to reach the products, as long as the initial and final conditions are the same.
The first step is to rearrange the given reaction in order to match the target reaction:
4NH3 + 5O2 - 4NO + 6H2O
Multiply through by the stoichiometric coefficients to balance the equation:
8NO + 12H2O - 8NH3 + 20O2
To match the target reaction NO + 3/2H2O - NH3 + 5/2O2, multiply through by the appropriate coefficients:
4NO + 6H2O - 4NH3 + 10O2
Now, you can compare the coefficients between the target reaction and the derived equation to determine the enthalpy change. In this case, the derived equation has equal coefficients, so the enthalpy change remains the same:
ΔH = -906 kJ
Therefore, the enthalpy change for the reaction NO + 3/2H2O - NH3 + 5/2O2 is -906 kJ, which is the same as the given reaction.