Tin is obtained from cassiterite by reduction with coke. Use the data given below to determine the minimum temperature (in K) at which the reduction of cassiterite by coke would take place.
At 298 K:ΔfH∘(SnO2(s))=−581.0 kJmol−1,ΔfH∘(CO2(g))=−394.0 kJmol−1
S∘(SnO2(s))=56.0JK−1mol−1,S∘(Sn(s))=52.0JK−1mol−1,S∘(C(s))=6.0JK−1mol−1,S∘(CO2(g))=210.0JK−1mol−1
Assume that the enthalpies and the entropies are temperature independent.
SnO2(s)+C(s)→CO2+Sn
ΔH=(ΔfH)P−(ΔfH)R
=(–394+581) kJ/mol
=+187 kJ/mol
ΔS=(S)P−(S)R
=(210+52)–(56+6) J/Kmol
=200 J/kmol
For any reaction to take place, ΔG<0
The minimum temperature is where ΔG=0
ΔG=0=ΔH−TΔS
187×1000–200T=0
T=935K