In: Chemistry
The criterion for a spontaneous chemical reaction is:
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 a) ΔrG < 0  | 
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 b) ΔrS = 0  | 
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 c) ΔrH > 0  | 
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 d) ΔrG = 0  | 
The criterion for sponataneous chemical reaction depend upon
G but not
H, and 
S.
Enthalpy: 
H = -ve,
spontaneous   
  
  
H = +ve,
non-spontaneous
H = 0,
equillibrium
but it is not criterion for spontaneous process in all cases
Entropy: 
S = +ve,
Spontaneous
S = -ve,
non-spontaneous
  
S = 0,
Equilibrium
but it is not criterion for spontaneous process in all cases
So, Gibbs freeenergy is introduced to explain spontaneity
G = 
H -
T
S
Gibbs freeenergy:
G = -ve,
spontaneous
G = +ve,
non-spontaneous
G = 0,
Equilibrium
So, by using Gibbs freeenergy is used to explain spontaneity of reaction by combining both enthalpy and entropy in all cases at all temperatures and pressures