*“Ready? State steady-state*

*Approximation (the*

*Famous, eponymous *

*Calc step involved):*

*Key intermediate’s*

*Change over time shows a *

*Negligibility;*

*Rate law resolves.”*

The 20 October 2021 Twitter poem was another posted in National Chemistry Week 2021. This poem highlighted another simplifying technique commonly used in chemical kinetic analyses, called the steady-state approximation, and it did so via a pseudo-double-dactyl structure.

**“Ready? State steady-state /**

**Approximation (the /**

**Famous, eponymous / **

**Calc step involved)…”**

The biggest challenge with this week of poems was identifying potential rhymes related to these often-math-centric concepts! The first line here grew out of considering the phrase “steady state.” The steady-state approximation takes its name from the “eponymous calc step involved”: a mathematical simplification relying on the idea that the concentration of a given reaction mechanism’s intermediate remains relatively consistent (steady).

**“Key intermediate’s /**

**Change over time shows a /**

**Negligibility; /**

**Rate law resolves.”**

In this simplified mechanism, a reactant forms an intermediate, which forms a product:

Reactant → Intermediate → Product

To monitor this reaction’s rate, we consider the appearance of the product over time. Without going too equation-heavily into the details, we can look at the big ideas.

The intermediate is typically in what is called a steady state: once the reactant forms an intermediate, that intermediate forms the product. The intermediate’s concentration stays relatively steady: relatively constant. Stepping briefly into calculus, the derivative of a mathematical function represents the change of that function over time. For a constant function, the derivative is zero.

Thus, the steady-state approximation is that the change in concentration of this intermediate over time is roughly equal to zero. Chemists use this approach and the steps that ensue to derive a rate law, finding the rate of the appearance of the product over time. The change in concentration of the intermediate over time is approximated as zero (it “shows a negligibility”), so the rate law is more easily calculated.

(This poem and essay obviously approximate several mathematical steps of their own; however, ideally, they provide an introduction to another kinetic concept useful to chemists.)

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