# What is first law of thermodynamics?

##### 1 Answer
Jul 16, 2018

The "First Law of Thermodynamics" is a version of the law of conservation of energy

It applies to old-style-stated versions of a thermodynamic system:

$\underbrace{\Delta U} {\setminus}_{\text{change in internal energy ") =underbrace(Q_("in"))\_("heat added") + underbrace(W_("on"))\_("work done on system}}$

As with all things thermo-dynamical, you have to dig a bit deeper to understand what that really means.