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(iii)The total entropy of the universe must tend to increase in a

spontaneous process.
(iv)It is not possible to convert heat into work without compensation.
(v)It is impossible to construct a heat engine of 100% thermal efficiency.

 Gibb’s Free energy(G):It is the energy available for useful work done.
G = H - T∆S
∆G = ∆H - T∆S

If ∆G = -ve, process is spontaneous.
If ∆G = +ve, process is non-spontaneous.
If ∆G = 0, process is at equilibrium state.

 Relationship between free energy and equilibrium constant:
o
∆G = ∆G + RTlnQ
At equilibrium, ∆G = 0 and Q = K
o
So, ∆G + RTlnK = 0
o
∆G = - RTlnK
o
∆G = -2.303 RTlogK
Where, Q – reaction quotient

K – equilibrium constant
∆G – Change in Gibb’s free energy
o
∆G – Standard Gibb’s free energy change
Third law of Thermodynamics:It has the following statements
(i)Entropy of a solid or liquid approach zero at the absolute zero
temperature.
(ii)Every substance has a finite positive entropy, but at absolute zero

temperature the entropy may become zero.