Question

So what is the main purpose of the First of Law of Thermodynamics? How is this related to another physical law? Also why is heat, energy and temperature different here?

Answer 1

First law of thermodynamics is a version of energy conservation. that is total energy of universe is constant. and the main purpose behind the law is that many power plants and engines operates by turning heat energy in works and that is how universe is operated .by knowing that the total energy will remain constant, we can easily deal with the power conservation.

change in temperature can be determine using heat and internal energy change . so here these three terms are different. because total energy change of the system will be equal to the heat transfer to the system + change in temperature.