Question

Consider the reaction:

2A (g) + 3 B (g) → 2 C (g) ΔHrxn = +254.3 kJ

What will be the enthalpy change (in kJ) if 0.812 mol B reacts in excess A?

Answer 1

The enthalpy change (in kJ) if 0.812 mol B reacts with excess A is +202.3 kJ. This can be calculated by first determining the number of moles of A that are needed to react with 0.812 mol B. Since the mole ratio of A to B is 2 : 3, the number of moles of A needed is 0.812 mol B x (2/3) = 0.5413 mol A. Then, the enthalpy change can be calculated as 0.5413 mol A x (254.3 kJ/2 mol A) = 202.3 kJ.