Anchoring chemistry.

I was reminded of this article by Michelle Francl[1], where she poses the question “What anchor values would most benefit students as they seek to hone their chemical intuition?” She gives as common examples: room temperature is 298.17K (actually 300K, but perhaps her climate is warmer than that of the UK!), the length of a carbon-carbon single bond, the atomic masses of the more common elements.

Well, one of my own personal favourites is anchoring chemical timescales. From 10^-18 s (that of electron dynamics, and presumably the fastest processes in chemistry) to 10⁺¹⁸ (approximately the age of the universe). And (for a unimolecular process) this can be reduced to this equation:  Ln(k/T) = 23.76 – ΔG^‡/RT I quoted this equation in a recent post, since it gives you the fastest possible chemical reaction if ΔG^‡ is set to zero (which of course is not a reaction but a vibration), but which gives you a good estimate of how fast a process will be for any given value of a barrier. It can of course also be solved for e.g. the required barrier to achieve a half-life equivalent to the age of the universe. So, perhaps in increments of orders of 3 magnitudes (of which there are 13 covering the above span) would anyone like to contribute either:

1. Their own favourite chemical anchor, or
2. Their own favourite example of a chemical timescale bounded by the above limits?

(I did start a list of the latter for our own students, but it is still pretty sparse!)

References

1. M. Francl, "Take a number", Nature Chemistry, vol. 5, pp. 725-726, 2013. http://dx.doi.org/10.1038/nchem.1733