Answer to Question #108799 in General Chemistry for Ariana

Question

1. What is a spontaneous process? Is the following process spontaneous or not?

a) Rusting of iron
b) Water evaporate at room temperature and standard pressure
c) CH4(g)+2 O2(g)→CO2(g)+2 H2O(l) ΔH°=−890.3 kJ
d) Oxygen condense at room temperature and standard pressure

Answer 1

A spontaneous process is one that occurs on its own, without any energy input from the outside. No intervention is required because these processes are thermodynamically favorable. The change in ΔG or the Gibbs function may be used to assess the spontaneity of a process. If ΔG is negative, the process is spontaneous

a) Rusting of iron is a spontaneous process. Happens slowly but by itself.

b) Water evaporate at room temperature and standard pressure - spontaneous! Same reason.

c) CH4(g)+2 O2(g)→CO2(g)+2 H2O(l) ΔH°=−890.3 kJ 

ΔG = ΔH - TΔS. As ΔH is negative for this prosses and much greater than the entropy change, so the overall ΔG change is negative. It proves that this process is spontaneous.

d) Oxygen condense at room temperature and standard pressure

the entropy of this process is increasing which is against the spontaneity of the process. Entropy factor for this condensation is greater than enthalpy.