“A reaction we call exothermic
Is the theme of this statement affirmic:
Wear your gloves in the lab
When the beaker you grab,
Lest you cause self a burn epidermic!”
The next few limericks, beginning with this one from 15 April 2019, address the concept of enthalpy. Enthalpy is a science-specific vocabulary word for the heat energy transferred during a constant-pressure process. Enthalpy is subtly different from other forms of energy; one of the upcoming poems will address this directly.
“A reaction we call exothermic/
Is the theme of this statement affirmic:”
As we saw with an earlier limerick, the energies of reactions are described by their own vocabulary words. This is the case for enthalpies of reaction as well; reactions can be characterized as exothermic or endothermic.
An exothermic reaction releases heat energy. In a chemist’s notation, we would write some variation of -𝛥H to communicate this, although the exact notation varies with specific conditions and conventions. Overall, the “negative delta H” tells us that this corresponds to a change in enthalpy during a process/reaction: this reaction releases heat energy, meaning the reactants are at higher enthalpic content than the products.
(An endothermic reaction has a “positive delta H,” or +𝛥H. This is analogous to the discussion of potential energy surfaces a few entries back; note the similar– but not identical– language of exothermic and endothermic, compared to exergonic and endergonic.)
In poetic terms, this limerick introduces exothermicity, then promises to explain a bit of what that term means, via a “statement affirmic”!
“Wear your gloves in the lab/ When the beaker you grab,/
Lest you cause self a burn epidermic!”
It is a best practice in a chemistry lab to wear disposable gloves when working with glassware, and one common piece of glassware is a beaker. Because exothermic reactions release heat, if you pick up a piece of glassware in which one is occurring, you should take particular precautions to wear your gloves, so as not to burn your hands: your skin “epidermic.” (That you should also be wearing safety goggles at all times in a chemistry lab goes without saying!)
Chemphasis 