For which of the following gaseous reactions is the change in enthalpy ( H ) exactly equal to the change in internal energy ( U ) at a constant temperature?

Step-by-step solution

The relationship between change in enthalpy ( H ) and change in internal energy ( U ) for a gaseous reaction at constant temperature is given by: H = U + n_g RT where n_g is the difference between the number of moles of gaseous products and the number of moles of gaseous reactants. For H to be exactly equal to U , the value of n_g must be zero. Evaluating n_g for the given reactions: For PCl₅(g) PCl₃(g) + Cl₂(g) , n_g = (1 + 1) - 1 = 1 For N₂(g) + 3H₂(g) 2NH₃(g) , n_g = 2 - (1 + 3) = -2 For N₂(g) + O₂(g) 2NO(g) , n