Question

Consider the reaction H2(g) + Cl2(g) → 2HCl(g)ΔH = −184.6 kJ / mol If 2.00 moles of H2 react with 2.00 moles of Cl2 to form HCl, what is ΔU (in kJ) for this reaction at 1.0 atm and 25°C? Assume the reaction goes to completion.

Answer 1

Answer:

ΔU=-369.2 kJ/mol.

Explanation:

We start from the equation:

Δ(H)=ΔU+Δ(PV), which is an extension of the well known relation: H=U+PV.

If Δ(PV) were calculated by ideal gas law,

PV=nRT

Δ(PV)=RTΔn.

Where Δn is the change of moles due to the reaction; but, this reaction does not give a moles change (Four moles of HCl produced from 4 moles of reactants), so Δ(PV)=0.

So, for this case, ΔH=ΔU.

The enthalpy of reaction given is for one mole of reactant, so the enthalpy of reaction for the reaction of interest must be multiplied by two:

$2 reactant moles*\frac{-184.6kJ}{mol}$

ΔU=-369.2 kJ/mol.