The First Law of Thermodynamics is really exciting, especially when we look at closed systems! 🚀

This law says that energy can’t be created or destroyed; it can only change forms. In closed systems, the internal energy (that’s what we call it: $U$) stays the same because no heat or work comes in or goes out from the outside.

Key Ideas:

• Energy Conservation: The total energy in the system stays the same.

• Internal Energy ($U$): Changes happen only inside the system.

• Work ($W$) and Heat Transfer ($Q$): For closed systems, both $Q$ (heat) and $W$ (work) are zero. This leads us to:

  $\Delta U = Q - W = 0$

Isn't it amazing to think about how the universe follows this important rule? Every little interaction and every change is part of it! 🌌