Question

One of the possible initial steps in the formation of acid rain is the oxidation of the pollutant SO2 to SO3 by the following reaction: SO2(g) + 1/2 O2(g) -> SO3(g) The reaction is exothermic, meaning that it is spontaneous at lower temperatures, but becomes nonspontaneous at higher temperatures. At what temperature does it change from being spontaneous to nonspontaneous?

Molecule ΔHf (kJ/mol) @ 25°C S (J/molK) @ 25°C

SO2(g) -296.8 248.2  

SO3(g) -395.7 256.8

503 K

1052 K

98.7 K

99.1 K

Answer 1

SO2(g) + 1/2O2(g) --------> SO3(g)

H0   = H0f products - H0f reactants

         = -395.7-(-296.8 + 1/2*0)

         = -98.9KJ/mole

        =-98900J/mole

S0   = S0f products - S0f reactants

          = 256.8-(248.2+205)

         = -196.4J/mole

G0 = 0 at equilibrium

H0 -TS0    = 0

H0   = TS0

T = H0 /S0

       = -98900/-196.4

     = 5036K

503K >>>>answer