What is the difference between thermodynamic and kinetic stability

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Physical Chemistry Chemical Physics , 22 7 , The reason is that the transition states along the lowest-energy reaction path have a much higher thermodynamic potential energy than the average kinetic energy of the reactants. The reactants are kinetically trapped - or stable just because they are stuck in a local minimum. The minimum amount of energy that you would need to provide in the form of heat a lit match to overcome that barrier is called the activation energy.

We can apply this to lots of other systems as well. One of the most famous and still extensively researched examples is glasses. Glasses are interesting because they are examples of kinetic stability in physical phases. Usually, phase changes are governed by thermodynamic stability. In glassy solids, the molecules would have a lower potential energy if they were arranged in a crystalline structure, but because they don't have the energy needed to get out of the local minimum, they are "stuck" with a liquid-like disordered structure, even though the phase is a solid.

Kinetics deals with all things that impact the rate at which a reaction occurs. One implication of that is that reaction kinetics are partially a function of the stability of the intermediate species and transition states that the pathway of a chemical reaction necessarily has to pass through en route to the formation of the final product.

If those intermediates are highly unstable i. In other words, thermodynamic stability is totally independent of the pathway between reactants and products. While it's true that thermodynamic stability is the ultimate arbiter of the spontaneity of a reaction, if the kinetics render the reaction too slow then, in practice, the reaction may not actually occur at all under some given set of conditions. The classic textbook example is the conversion of diamond to graphite, which is thermodynamically favorable because the free energy of graphite is lower, but doesn't occur under ordinary conditions because the kinetics of the reaction in the form of the immense activation energy required are extremely unfavorable.

Pathway 1 has much higher activation energy than Pathway 2, but the final products at the end of Pathway 1 are lower in free energy i. This means that Pathway 1 is thermodynamically favored, but Pathway 2 is kinetically favored that is, it poses a lower barrier in terms of activation energy and the reaction will proceed more rapidly via this pathway.

The consequence of this is that the kinetic pathway, Pathway 2, will be the favored one, unless environmental conditions temperature, pressure, concentrations of catalysts, etc.

In summary, thermodynamic stability in terms of free energy difference between reactants and products will determine whether a given reaction could be theoretically spontaneous, but kinetic factors will decide whether the reaction occurs in practice under the given environmental conditions, as well as which pathway for a given reaction takes primacy.

There is often a "reaction barrier" that needs to be overcome. Thus one must supply energy to get the reaction started, but once started it becomes self-sustaining.

One can think of it this way: one has to break bonds in a reaction before one can make bonds. Energy is needed to break the first bonds. Then making new bonds can supply enough energy to keep the reaction going.

Note that I'm talking about thermodynamically allowed reactions. If a reaction is not thermodynamically allowed, then even if some bonds are broken by adding energy, the reaction will not spontaneously continue. Kinetic - how unwillingly something reacts. Thermodynamic - the energies involved, amount of gradient.

For example, aluminium metal is kinetically much more stable than iron metal in damp air it doesn't rust , but thermodynamically much less stable if it did oxidise, it would give out more energy.

You are thermodynamically unstable in air, but don't worry, you're not going to spontaneously combust, which is another way of saying that you are kinetically stable. Kinetic stability refer to a pre equilibrium conditions. For example the equilibrium constant K may be very large meaning the formation of the product is favorable, but the condition is such that the reaction does not go or goes extremely slowly Thermodynamic stability refer to a system in which products formation is not favourable.

For example we have larger reaction quotient Q. A reaction can be thermodynamically unstable but kinetically stable because the condition are such that the rate of the reaction is zero. A mixture of coal and oxygen are kinetically stable because the condition for combustion are not obtained until the coal is heated to its ignition temperature. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.

Create a free Team What is Teams? Thermodynamically stable. Post by » Sun Feb 23, pm I understand that kinetics deals with the rate of a reaction and thermodynamics deals with whether the rxn is forward or backwards. Re: Kinetically stable vs. Post by JD » Mon Feb 24, am Kinetic stability basically occurs when the reactants react really slowly.

The slower the reaction occurs, the greater the kinetic stability. If you say, "This reaction is kinetically stable," then that implies that the reaction occurs very slowly. Thermodynamic stability depends on whether or not the reaction is spontaneous. A thermodynamically stable reaction is one that basically does not react. As a result, it is independent of the pathway between reactants and products.