Question

Exercises: 3. Given the following two thermochemical equations, determine the AHºrxn,unknown. N2(g) +2 02(g) – 2 NO2(g) AH®rxn= 67 kJ NO(g) + 12 02(g) → NO2(g) AHºrxn=-56 kJ 4N2(g) + 402(g) → NO(g) AHºrxn,unknown= ? 4. Given the following two thermochemical equations, determine the AHrxn,unknown. Fe2O3(s) + 3 CO(g) – 2 Fe(s) + 3 CO2(g) AH°rxn=-26.7 kJ CO(g) + 42 02(g) → CO2(9) AH°rxn=-283.0 kJ 2 Fe(s) + 3/2 02(g) → Fe2O3(s) AHºrxm,unknown=?
please help, i dont understand and need steps explainsd as well thank you

Answer 1

3)
Lets number the reaction as 1, 2, 3 from top to bottom
required reaction should be written in terms of other reaction
This is Hess Law
required reaction can be written as:
reaction 3 = +0.5 * (reaction 1) -1 * (reaction 2)

So, ΔHo rxn for required reaction will be:
ΔHo rxn = +0.5 * ΔHo rxn(reaction 1) -1 * ΔHo rxn(reaction 2)
= +0.5 * (67.0) -1 * (-56.0)
= 89.5 KJ
Answer: 89.5 KJ

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