I was reminded of this article by Michelle Francl, 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:
- Their own favourite chemical anchor, or
- 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!)
- M. Francl, "Take a number", Nature Chemistry, vol. 5, pp. 725-726, 2013. http://dx.doi.org/10.1038/nchem.1733