Chem Enthalpy for reaction problem

Question

Hello! Struggling a little with this problem and not sure if i am doing it right.

The experiment was performed at a constant pressure at 298K using 0.300 mol of A (g) and 0.350 mol of B (g) in a closed, flexible container. The chemist measured these energy changes in the system during the reaction:

Reaction: 3A (g) + 4B(g) = A3B4(s)

1. q_system = 2.7 kJ
2. w_PV = 0.324 kJ

Calculate the enthalpy change per kJ/molørxn.

------since i know that under constant pressure ∆U = ∆H = q + w , i have found that the ∆H = 2.7 + 0.324 = 3.024, and then divide the 3.024 by 3 and same for by 4. Then I would add those up and get the enthalpy for the reaction. Is that right or I need to just divide by the mols of limiting reagent which is A (0.300 mol) and that would be the answer?

Thank you in advance

Answer 1

Since you calculated the enthalpy change as 3.024 kJ. Divide 3.024 kJ by the moles of product produced because we are looking for the enthalpy change per mole of product.

1) Find # moles produced as a result ofl limiting reagent

the mole of product produced will either be 0.300 mole A*(1 mole A3B4/3 mole A) to give 0.1 mole A3B4 or

0.350 mole B*(1 mole A3B4/4 mole B) to give 0.0875 mole A3B4

00875 mole is smaller than 0.1 mole, thus B is the limiting reagent.

2) Find molar enthalpy

Molar enthalpy, or enthalpy per mole of product is 3.024 kJ/00875 mole, which is 34.56 kJ/mole