First Law of Thermodynamics States that,Energy can neither be created nor be destroyed, it can be only converted from one form to another.

Limitations of 1st Law Of Thermodynamics
1) As it says energy can be converted from one form to another, it don't states how and how much energy is converted.

2) Suppose electrical energy is converted into heat by means of heater, and if same amount of heat is given to heater, it will not generate that amount of electricity. That is low is unidirectional.

3) The Law don't consider losses in conversion.
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1st Law states that the energy remains conserved but it doesn’t indicate

1. The direction of heat transfer.
2. The conditions under which heat can be converted into work.
3. It doesn’t tell why the whole of heat energy cannot be converted into mechanical work.
4. There are many irreversible process occur in nature. 1st law cannot explain the lack of reversibility ex: heat flows naturally from a hot body to cold body but heat will never of itself flow from a cold body to a hot body.
Source(s):
http://www.examville.com

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One important thing to realize about thermodynamics is that it is all about averages for huge numbers of things (atoms, molecules, etc.). So all of the "laws" of thermodynamics are talking about average behavior - like the second law that says entropy of a closed system cannot decrease. If the system is small enough (it has to be pretty small - like a few molecules), different laws can come into play, like quantum mechanics and other swear words in graduate physics departments. :-)
The first law is pretty solid - it is the first law, after all. But even it is "wrong" - we all know that nuclear fission and fusion reactions can transform matter into energy, effectively creating energy in a closed system!
Source(s):
Just from my experience learning and teaching thermodynamics and other unmentionable subjects in university.

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