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