To use Hess's law, we need to manipulate the given equations so that they add up to the desired equation:
N2O5 (g) rightwards arrowNO3 (g) + NO2 (g) (multiply by 1)
2NO3 (g) + O2 (g) rightwards arrow2O3 (g) + 2NO2 (g) (multiply by 2 and flip the direction)
O3 (g) + 2NO2 (g) rightwards arrowN2O5 (g) + O2 (g) (add the two equations)
Now we can add the enthalpies of the individual reactions to get the total enthalpy change for the desired reaction:
ΔH = ΔH1 + ΔH2
ΔH1 = +44.3 kJ (from the first equation)
ΔH2 = -20.1 kJ (from the second equation, multiplied by 2 and flipped)
ΔH = +44.3 kJ - 2(-20.1 kJ) = +84.5 kJ
Therefore, the enthalpy change for the reaction O3 (g) + 2NO2 (g) → N2O5 (g) + O2 (g) is +84.5 kJ.
Using Hess law, calculate ΔH for the equation: O3 (g) +2NO2 (g)→ N2O5 (g) + O2 (g)
Given the following equations:
N2O5 (g) rightwards arrowNO3 (g) + NO2 (g) ΔH=+ 44.3 kJ
NO3 (g) + O2 (g) rightwards arrowO3 (g) + NO2 (g) ΔH=-20.1kJ
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