Question

Calculate the temperature (in ºC) to which silver ore, Ag₂O, must be heated to spontaneously decompose the ore to oxygen gas and solid silver metal at standard state. (ΔHº_f of Ag₂O(s) = –31.05 kJ/mol;  Sº values: Ag(s), 42.55 J/mol•K; O₂(g), 205.1 J/mol•K; Ag₂O(s), 121.3 J/mol•K)

234 ºC

843 ºC

374 ºC

467 ºC

195 ºC

Answer 1

Ag2O(s) ------------> 2Ag(s) + 1/2O2(g)

ΔHº     = ΔHº_f products - ΔHº_f reactants

          = 1/2*0 + 2*0 - (-31.05)    = 31.05KJ/mole

ΔSº     = Sº_f products - Sº_f reactants

             = 1/2*205.1 + 2*42.55 - (121.3)

              = 102.55 +2*42.55 - (121.3)   = 66.35J/mole   = 0.06635KJ/mole-K

ΔGº    = ΔHº -TΔSº

ΔGº <0 for spontaneous reaction

ΔGº <0

ΔHº -TΔSº <0

ΔHº <TΔSº

ΔHº /ΔSº <T

31.05/0.06635<T

468K<T

195⁰C<T

195⁰C >>>>>answer