Q.(a) State the various statements of Second law of Thermodynamics. OR

The Second Law of Thermodynamics has several equivalent statements (Clausius, Kelvin-Planck, and the entropy formulation), all expressing that natural processes proceed in a direction that increases the total entropy of the universe. (This answers part (a) of the OR question.)

1. Clausius Statement:

   "It is impossible for heat to flow, of itself, from a colder body to a hotter body without the aid of external work." Heat spontaneously flows only from hot to cold; making it flow the other way (as in a refrigerator) requires work input.

2. Kelvin-Planck Statement:

   "It is impossible to construct a machine (engine) that, operating in a cycle, produces no effect other than the absorption of heat from a single reservoir and its complete conversion into an equivalent amount of work." In other words, no heat engine can be 100% efficient -- some heat must always be rejected to a colder sink.

3. Entropy Statement (most general, modern form):

   "Every spontaneous (natural, irreversible) process is accompanied by an increase in the total entropy of the universe (system plus surroundings); Delta-S(universe) > 0 for a spontaneous process, and Delta-S(universe) = 0 only for a reversible process."

4. Ostwald's statement (a variant): …