Laws of Svante Arrhenius

Ever since school, everyone knows that the rate of chemical reactions increases with increasing temperature and, conversely, the lower the temperature, the lower the reaction rate. These laws of Svante Arrhenius were introduced to the rank of fundamental in 1889 and laid the foundations of one of the most important branches of chemistry - chemical kinetics, which studies the rates and mechanisms of reactions.

These laws of Svante Arrhenius were introduced to the rank of fundamental in 1889 and laid the foundations of one of the most important branches of chemistry - chemical kinetics, which studies the rates and mechanisms of reactions

To join the reaction, atoms or molecules must come together as close as possible. But to do this they are hampered by electric repulsive forces acting between like-charged electron shells of atoms and molecules - the so-called potential barrier. It can be overcome only by jumping. But it is possible to do this only to those particles that have sufficient energy for this - it is called the activation energy. It's something we tell the particles, heating up the reacting mixtures. The more heated the mixture, the more active the particles, more easily "jumping over" the barriers separating them from each other. And conversely, near the absolute zero temperature (-2730 C), the thermal motion of atoms and molecules fades, and therefore the speed of any chemical reaction tends to zero.

The laws of Svante Arrhenius were confirmed by thousands of experiments in the widest range of temperatures, while scientists were not interested in energy chain reactions at low temperatures...

An example of such reactions is polymerization - the formation of long chains consisting of many identical units of monomer molecules. The first act of reaction - the nucleation of a chain - begins with the fact that one or more chemical bonds are broken in the initial monomeric molecule. To break the chemical bond, energy is needed. Therefore, the first act of the polymerization reaction is an endothermic process, i.e. going with the supply of energy from the outside. Due to this, the molecule can attach to itself exactly the same molecule. As a result of the addition of the next molecule to the chain, energy is already generated in this place - the growth of the chain is an exothermic process. Energy is as it were transferred from one link to another. You just need to "bring a match", give the first push to the chain process.

But will the laws of Svante Arrhenius stand if the mixture of reagents is at a low temperature, and the energy for the fuse of reaction is brought in the form of a portion of ionizing radiation? For the experiments, formaldehyde frozen to liquid helium temperature of 40 K (-2690 C) was used and irradiated with radioactive cobalt-60. The result was absolutely indisputable - individual molecules of formaldehyde were combined into long polymer chains! In confirmation of this, scientists measured the amount of radiation energy transferred to the substance, and counted the number of links in the polymer chain. It turned out that for every 100 electron-volts of spent energy, up to 1000 molecules were connected to the polymer, whereas in simple, non-chain reactions there are no more than two or three molecules per the same amount of energy spent. Hence, ionizing radiation really only "ignites" the reaction, which goes on by itself.

It was found that the energy released at the time of linking the link to the circuit is clearly small, so that the next molecule can approach the circuit to the required distance and join it. Then, how do molecules connect, overcoming the potential barrier?..

It turns out that the laws of Svante Arrhenius cease to be valid at very low temperatures: - 100 K. The rapid drop in the rate of chemical reactions decreases gradually as the temperature decreases, and then... the speed becomes almost constant! And the laws of quantum mechanics help to overcome a potential barrier to a molecule: a molecule can go not only over the barrier, but also... through it! Physicists know that small particles (electrons, nucleons, nuclear fragments) can leak (tunnel). Here we are talking about real mastodons - huge compared to the nuclei of organic molecules. The probability of tunnel transitions due to their large mass is very small. They begin to tunnel only at very low temperatures, when the usual above-barrier transitions are completely impossible.

Perhaps, despite the laws of Svante Arrhenius, somewhere in space, a similar synthesis of complex protein chains of macromolecules occurs and thus a new life is born...