Finding Work and Value of ΔE?

Question

Calculate the work (w) and ΔE^o, in kJ, at 298 K and 1 atm pressure, for the combustion of one mole of C₃H₈ (g). First write and balance the equation. The products will be CO₂ (g) and H₂O (g).

The value of ΔH^o for this reaction is -2043.9 kJ/mol.

The value for w in kJ = 

The equation for work is given by: w = -P_extΔV.

The value for ΔE^o ( in kJ) =

Answer 1

C₃H₈(g) + 5O₂(g) ==> 3CO₂(g) + 4H₂O(g) ... balanced equation for complete combustion

w = -P∆V @ constant pressure

So first, we must find the ∆V, i.e. the change in volume when 1 mole of C₃H₈ is combusted:

Since we are operating at STP (constant temp and pressure), we can take the ∆V as the change in moles of gas from reactant to product side. We have 6 moles of gas on the reactant side and 7 moles of gas on the product side, so the ∆V = 7 - 6 = 1 L.

w = -P∆V = -(1 atm)(1 L) = - 1 L-atm x 101.325 J/1 L-atm = -101.325 J

∆E = ∆H - P∆V

∆E = -2043.9 kJ - (-0.1 kJ) = -2043.8 kJ