1
Question
4Fe(s)+3O2(g)→2Fe2O3(s)
For the following reaction, ΔS=−549.4 J K−1 mol−1 at 298 K. ΔrH⊖=−1648×103 J mol−1
The reaction is spontaneous
For the following reaction, ΔS=−549.4 J K−1 mol−1 at 298 K. ΔrH⊖=−1648×103 J mol−1
The reaction is spontaneous
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Solution
The correct option is A True
One decides the spontaneity of a reaction by considering ΔSTotal(ΔSsys+ΔSsurr). For calculating ΔSsurr, we have to consider the heat absorbed by the surroundings which is equal to −ΔrH⊖. At temperature T, entropy change of the surrounding is
ΔSsurr=−ΔrH⊖T (at constant pressure)
=−(−1648×103 J mol−1)298 K
=5530 J K−1 mol−1
Thus, total entropy change for this reaction
ΔrStotal=5530 J K−1 mol−1+(−549.4 J K−1 mol−1)
=4980.6 J K−1 mol−1
This shows that the above reaction is spontaneous.
True
One decides the spontaneity of a reaction by considering ΔSTotal(ΔSsys+ΔSsurr). For calculating ΔSsurr, we have to consider the heat absorbed by the surroundings which is equal to −ΔrH⊖. At temperature T, entropy change of the surrounding is
ΔSsurr=−ΔrH⊖T (at constant pressure)
=−(−1648×103 J mol−1)298 K
=5530 J K−1 mol−1
Thus, total entropy change for this reaction
ΔrStotal=5530 J K−1 mol−1+(−549.4 J K−1 mol−1)
=4980.6 J K−1 mol−1
This shows that the above reaction is spontaneous.
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