Question

When two moles of H2 and one mole of O2 react to produce two moles of
gaseous water at 373 K and 1 bar pressure, a total of 484 kJ are evolved.
What are (a) Δ H and (b) Δ U for the production of a single mole of H2O (g).

Answer 1

Answer:

ΔH = -237 KJ

ΔU = -235.45 KJ  mol–1

Explanation:

You know that when 2 moles of hydrogen gas react with 1 mole of oxygen gas, you get 2 moles of water and 484 kJ of heat are evolved

2H2(g)+O2(g)→2H2O(l) ΔH=−484 kJ.

Now, in order for this reaction to produce 1 mole of water, all the coefficients of the chemical equation must be halved

ΔH1 mole H2O=1/2⋅ΔH2 moles H2O

ΔH1 mole H2O = 474/2

ΔH = -237 KJ

 U =  H – n RT

 U = (-237000) –(-1/2)( 8.314) (373)

      = -237000 + 1550.5

     = -235450

    = -235.45 kJ mol–1