Question

Given the following thermochemical data:

½H2(g)+AgNO3(aq) → Ag(s)+HNO3(aq) ΔH = -105.0 kJ

2AgNO3(aq)+H2O(l) → 2HNO3(aq)+Ag2O(s) ΔH = 44.8 kJ

H2O(l) → H2(g)+½O2(g) ΔH = 285.8 kJ

Use Hess’s Law to determine ΔH for the reaction: Ag2O(s) → 2Ag(s)+½O2(g)

Answer 1

½H_2(g) + AgNO_3(aq) → Ag_(s) + HNO_3(aq) ΔH = -105.0 kJ ....................1

2AgNO_3(aq) + H2O_(l) → 2HNO_3(aq) + Ag₂O_(s)  ΔH = 44.8 kJ .....................2

H₂O_(l) → H_2(g) + ½O_2(g) ΔH = 285.8 kJ ......................3

multyply to reaction 1 by 2 we get reaction

H_2(g) + 2AgNO_3(aq) → 2Ag_(s) + 2HNO_3(aq) ΔH = -210.0 kJ ....................4

wright down reactiion 2 in reverse manner we get reaction

2HNO_3(aq) + Ag₂O_(s)   →  2AgNO_3(aq) + H2O_(l)  ΔH = -44.8 kJ .........................5

now add reaction 3,4 and 5

reactant side  H2O_(l) of reaction 3 cancel product side  H2O_(l) of reaction 5

product side H_2(g) of reaction 3 get cancel by reactant side H_2(g) of reaction 4

reactant side 2HNO_3(aq) of reaction 5 get cancelled by product side 2HNO_3(aq) of reaction 4

and sum of all H give following reaction

Ag₂O_(s) → 2Ag_(s)+½O2_(g) H = 31 KJ