# Why do we use Δ to mean heating?

To express heating, we usually use $$\Delta$$ over reaction arrows like \begin{align} \ce{CaCO3 ->[\Delta] CaO +O2}. \end{align} Why do we use $$\Delta$$ to mean heating during chemical reactions? I thought up with one idea that $$\Delta$$ symbolizes fire. But actually I have no information about the origin of this usage. Does anybody know the origin or reason of this usage of $$\Delta$$?

• Good question, I would like to know how widespread the triangle is as symbol for heating – Nuclear Chemist Dec 2 '18 at 18:48
• It's (rather incorrect) short of $\Delta$T. – Mithoron Dec 2 '18 at 18:50

Δ symbolizes difference. For chemical reactions, it's usually difference between energy that reactants already have and energy needed for reaction. Then Δ = $$E_a$$ - activation energy of the reaction. Activation energy is like a "potential barrier" for reaction to happen. And Δ means that we've added this amount of energy so energy of reactants changed by Δ (difference).