Kinetic Thermodynamic Products
Kinetic Thermodynamic Products - Related Videos
02:38
Third Law of Thermodynamics
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2020
A pure, perfectly crystalline solid possessing no kinetic energy (that is, at a temperature of absolute zero, 0 K) may be described by a single microstate, as its purity, perfect crystallinity,and complete lack of motion means there is but one possible location for each identical atom or molecule comprising the crystal (W = 1). According to the Boltzmann equation, the entropy of this system is zero. This limiting condition for a system’s entropy represents the third law of thermodynamics: the...
02:16
First Law of Thermodynamics
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2020
Energy Conservation Energy can be converted from one form into another, but all of the energy present before a change occurs always exists in some form after the change is completed. This observation is expressed in the law of conservation of energy: during a chemical or physical change, energy can be neither created nor destroyed, although it can be changed in form. According to the law of conservation of matter, there is no detectable change in the total amount of matter during a chemical...
00:37
First Law of Thermodynamics
0 Views •
2019
The First Law of Thermodynamics states that energy cannot be created or destroyed, only transformed. This can be demonstrated within a classic food web where light energy from the sun is harnessed as radiant energy by plants, converted into chemical energy, and stored as complex carbohydrates. The vegetation is then consumed by animals and during the digestion process, the sugars release energy as heat. The sugars also produce chemical energy that either gets used up doing work, stored in...
02:49
Second Law of Thermodynamics
0 Views •
2020
In the quest to identify a property that may reliably predict the spontaneity of a process, a promising candidate has been identified: entropy. Processes that involve an increase in entropy of the system (ΔS > 0) are very often spontaneous; however, examples to the contrary are plentiful. By expanding consideration of entropy changes to include the surroundings, a significant conclusion regarding the relation between this property and spontaneity may be reached. In thermodynamic models, the...
00:53
Second Law of Thermodynamics
0 Views •
2019
The Second Law of Thermodynamics states that entropy, or the amount of disorder in a system, increases each time energy is transferred or transformed. Each energy transfer results in a certain amount of energy that is lost—usually in the form of heat—that increases the disorder of the surroundings. This can also be demonstrated in a classic food web. Herbivores harvest chemical energy from plants and release heat and carbon dioxide into the environment. Carnivores harvest the chemical energy...
FAQs
The pathway with the lower activation energy can produce its product more rapidly, giving that product an early advantage when the reaction is under kinetic control. Product stability becomes decisive only when the reaction can proceed reversibly and the products can interconvert. Thus, observed selectivity may reflect either the speed of formation or the relative stability reached after equilibration.
Reversibility allows initially formed products to return to reactive intermediates or starting materials and form alternative products. With sufficient opportunity for interconversion, the product distribution can shift toward the more stable product rather than preserving the product formed first. Without conditions that permit this equilibration, the faster pathway can remain dominant even if its product is less stable.
Lower temperatures or shorter reaction times generally favor the product formed through the faster pathway, because there is less opportunity for competing processes and product interconversion to alter the initial distribution. Conditions that permit equilibration can instead favor the more stable product. Temperature and time therefore serve as practical variables for shifting selectivity between kinetic and thermodynamic outcomes.
Chemists first consider whether the competing pathways differ mainly in formation rate, product stability, or both. To favor the faster-forming product, they can use lower temperature or a shorter reaction time when those conditions support kinetic control. To favor the more stable product, they need conditions that allow reversibility, interconversion, and equilibration before the reaction is stopped.
A product ratio that changes with temperature or reaction time can indicate whether selectivity is controlled by formation rate or by later equilibration. Early product distributions may emphasize the lower-activation-energy pathway, whereas distributions observed after reversible interconversion may reflect relative product stability. Comparing these outcomes helps chemists interpret competing pathways and identify conditions that control selectivity.
The distinction is useful whenever a reaction can produce alternative outcomes through competing addition, substitution, or elimination pathways. Chemists apply it when predicting which product will predominate and when optimizing a synthetic route. Selecting temperature, reaction time, and conditions that either limit or permit equilibration can improve control over the desired product and overall reaction selectivity.