Hess's Law: Why You Can Add and Subtract Reactions Like Equations Here's where most students get stuck with Hess's Law: not the concept itself, but trusting it enough to actually use it in an exam. The rule sounds almost too convenient — add up two reactions, and somehow you know the enthalpy of a third one you never even ran? It feels like a trick. It isn't. Once you see why it works, you stop memorizing it and start just... using it. What Hess's Law Actually Says The enthalpy change of a reaction is the same no matter how many steps you take to get there — one giant leap or five smaller ones, the total energy change is identical. That's it. That's the whole law. Why This Isn't Magic — It's Just Physics Enthalpy is a state function . That word gets thrown around a lot without explanation, so here's the plain version: a state function only cares about where you started and where you ended up — not the path you took. Think of it like al...
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