“A route’s back-and-forth versatility:
A question again for agility
Of arrow notation:
Tell-tale variation
Can indicate reversibility.”
The 18 April 2023 Twitter limerick continued a sequence of poems that aimed to highlight different types of arrows used in chemistry communication.
“A route’s back-and-forth versatility: /
A question again for agility /
Of arrow notation…”
We typically consider reactions as going only in the forward direction, from Point A to Point B, from reactants to products. However, it is more precise to say most reactions are reversible, so that either direction (Point A to Point B…OR Point B to Point A!) can technically be favored by considering the reaction conditions of interest. (Varying the temperature, pressure, and amounts of species involved in the reaction equilibrium would be a few ways to achieve this.)
This aspect of a chemical reaction (“the route’s back-and-forth versatility”) can be specifically shown in a few ways. The most characteristic denotation is two half-headed arrows, one pointing left and one pointing right, stacked on top of one another. That is, rather than A → B, we would write A ⇌ B. We would describe this reaction as “shifting left” if the pertinent conditions tended to form more of species A or “shifting right” if the pertinent conditions tended to form more of species B.
“Tell-tale variation /
Can indicate reversibility.”
This poem and the next few will highlight increasingly specific notation variations that indicate increasingly specific chemical principles: in this case, the “tell-tale” reaction arrow of interest highlights the reversibility of the reaction. The double-headed arrow tells us something different than a “left-to-right” arrow would.
As with last week, this post will be relatively brief, since the aim of each limerick in this series is simply to highlight (and describe) how the featured type of arrow is distinct from the others.
Chemphasis 