Sam asked in Science & MathematicsChemistry · 6 years ago

Determine the change in enthalpy for the following reaction at 25 C?

NO(g) + O(g) "goes to" NO2(g)

What is the change in enthalpy for this reaction given the following reactions:

2O3(g) "goes to" 3O2 H= -427kJ

2O(g) "goes to" O2(g) H= -495kJ

NO(g) + O3(g) "goes to" NO2(g) + O2(g) H= -199kJ

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  • BII
    Lv 7
    6 years ago
    Favorite Answer

    Hess’s Law: http://en.wikipedia.org/wiki/Hess%27s_law

    Start with C as it has NO on the correct side

    NO(g) + O3(g) → NO2(g) + O2(g)

    Remove O3 by subtracting ½A

    C-½A: NO + O3 - O3 → NO2 + O2 -1.5O2

    NO→ NO2 - ½O2

    Now add ½B to eliminate O2 RHS and adding O to LHS

    NO + (½×2)O → NO2 - ½O2 + ½O2

    NO + O → NO2 (success!)

    Hence eqn ΔHrxn = ΔH(C - ½ΔH(A) + ½ΔH(B)

    ΔHrxn = -199 – (0.5×-427) + (0.5×-495)

    ΔHrxn = -199 + 213.5 – 247.5 = -233 kJ

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