What are the limitations of First law of Thermodynamics?

(i) The first law of thermodynamics does not tell us anything about the extent and direction of the convertibility of one form of energy into another. For example when two bodies which are capable of exchanging heat energy are brought into contact. First law tells only that heat gained by one must be equal to that lost by the other, but it does not tell us which of the two would lose or gain heat energy. It also does not tell us how much heat energy would be transferred from one to the other.

(ii) It provides no information regarding the feasibility of the process.