First law of thermodynamics?

It is know as the law of conservation of energy. Mathematically, it can be written as ΔE = q – w, where E= internal energy, q = heat absorbed by the system and w = work done by the system.
Here are various statements of the first law of thermodynamics,
1) “Energy may be converted from one form to another, but it is impossible to create or destroy it.”
2) “There is an exact equivalence between the amount of work overcome and heat generated”–by Joule.
3) “When work is changed into heat or heat into work, the quantity of work is mechanically equivalent to the quantity of heat” — by Maxwell.
4) Energy of an isolated system must remain constant, although it may be changed from one form to another.
5) Energy in one form, if it disappears it will make its appearance in an exactly equivalent quantity in another form.
6) It is impossible to construct a perpetual motion machine that could produce work without any energy being consumed.

Source(s):
http://en.wikipedia.org/