gen-briefly-explain-the-first-law-of-thermodynamics-and-one-comm-dca0

Briefly explain the first law of thermodynamics and one common misconception about it.

## First Law of Thermodynamics The first law states that **energy cannot be created or destroyed, only converted from one form to another**. Mathematically, it's expressed as ΔU = Q - W, where the change in a system's internal energy (ΔU) equals the heat added to it (Q) minus the work done by it (W). ## Common Misconception **Misconception:** "The first law means energy is always conserved in any process, so we can achieve 100% efficiency in engines and never 'lose' energy." **Reality:** While total energy is always conserved, it doesn't remain *useful*. Energy often converts to low-quality forms (like waste heat) that can't easily do work. This is why engines can't be 100% efficient—not because energy disappears, but because it transforms into forms we can't fully harness. This limitation is actually addressed by the *second* law of thermodynamics (entropy).