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Chemists and Parents compared, Kinetically speaking

Are we there yet?

Are we there yet? Are we there yet? Are we there yet? Are we there yet?...

Have you ever uttered or heard the phrase: Are we there yet? or How much longer?  Does this prompt flashbacks of your last family vacation!?  We are constantly interested in time, and how fast things happen. Chemists are no different, we merely change the phrasing to: Is it done yet, and how much longer?Parents often appease their children with various games like, counting landmarks, finding different types of objects, watch the distance signs or mile markers, play I spy…anything that will distract them from the passage of time.

Chemists count the number of drops, watch the temperature or play I spy TLC (Thin Layer Chromatography). We even count the “mile” markers by measuring the change of concentration with time.

Like car trips, some reactions are very fast while others seem exceptionally slow. Kinetics relies on the relationship between the change in concentration versus time.  There are different techniques to study both types. Slower reactions are commonly followed by taking samples at different intervals and analyzing them.

Fast reactions though present a problem. What if the reaction is so fast that a sample can’t be taken fast enough? Never fear, where there is a will there is a way and chemists have come up with techniques to overcome this obstacle: the flow and pulse method discussed in section 9.5 of the Physical Chemistry text book.

Stopped Flow

Click to enlarge

The flow method involves both delivering the reactants into the vessel and mixing them quickly. The individual species are placed into separate chambers and then delivered rapidly into a mixing chamber. They are then transported down a tube that has some type of detector to follow the progress of the reaction.

While the flow method can both deliver and mix the reactants in fractions of a second, there are some reactions that require an even faster method. The pulse method relies on a system that is already at equilibrium and then with a “pulse” it changes conditions and the system can be monitored as it reestablishes equilibrium.

Both ultrasonic and nuclear magnetic resonance (NMR) spectroscopy can also be used in the study of these exceptionally fast reactions.

Like any road trip, there will be inquisitive children that ask the question ‘how long will it take?’ and adults will find creative ways to answer it.

Luckily, most chemists happen to be both adults and creative. Right?

Written by: jollshar

Sharlene Jolley has authored 20 more articles.

I received my graduate degree in organic chemistry from Kansas State University and have been teaching undergraduate chemistry courses for over 15 years. I strongly believe that you are never too old or young to learn and appreciate science and have had students ranging in ages from 5 to 65. Along with my college classes, I regularly teach science in K-12 classes and for special interest groups.

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