I am learning the basics of Thermodynamics.
Everywhere I read about the first law, it states "conservation of energy", and talks about how change in internal energy equals heat and work transfer.
I am aware of work transfer being considered positive and negative depending on the point of view we want to set.
That is okay.
But it confuses me to see the word "conservation".
If we take a very simple or at least very common real process like putting a plastic bottle completely filled with liquid water into a freezer (or whatever environment that is constantly under 273 K) and wait for thermal equilibrium to happen, the bottle will have expanded because water will have frozen increasing its volume and pushing the bottle's limits.
In this case:
The system (the bottle) has lost or given away a whatever amount of heat and it will also have generated a work transfer (to make the bottle expand).
It doesn't matter if we consider that work positive once or negative twice, in both cases energy has left the system in the form of work.
The total amount of internal energy of the system has clearly decreased.
So apparently there isn't really any "conservation" happening.
I do not intend to hate on thermodynamics, it's actually beautiful, I just want to understand the semantics.
I read other similar questions like this one, but in none did I find a clear answer.