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In chemistry, initiation is a chemical reaction that triggers one or more secondary reactions. Initiation creates a reactive centre on a molecule which produces a chain reaction . [ 1 ] The reactive centre generated by initiation is usually a radical , but can also be cations or anions . [ 2 ]
Initiation steps are classified according to the way that energy is provided: thermal initiation, high energy initiation, and chemical initiation, etc. Thermal initiation uses molecular thermal motion to dissociate a molecule and form active centers. High energy initiation refers to the generation of chain carriers by radiation.
Diverse methods are employed to manipulate the initiation, propagation, and termination rates during chain polymerization. A related issue is temperature control, also called heat management, during these reactions, which are often highly exothermic. For example, for the polymerization of ethylene, 93.6 kJ of energy are released per mole of ...
For example, the mass of a sample is an extensive quantity; it depends on the amount of substance. The related intensive quantity is the density which is independent of the amount. The density of water is approximately 1g/mL whether you consider a drop of water or a swimming pool, but the mass is different in the two cases.
For chain-growth polymerization, the overall activation energy is = +, where i, p and t refer respectively to initiation, propagation and termination steps. The propagation step normally has a very small activation energy, so that the overall value is negative if the activation energy for termination is larger than that for initiation.
Although thermal degradation is defined as an oxygen free process it is difficult in practise to completely exclude oxygen. Where this is the case thermal oxidation is to be expected, leading to the formation of free radicals by way of hydroperoxides. These may then participate in thermal degradation reactions, accelerating the rate of breakdown.
Thermochemistry is the study of the heat energy which is associated with chemical reactions and/or phase changes such as melting and boiling.A reaction may release or absorb energy, and a phase change may do the same.
In polymer chemistry, anionic addition polymerization is a form of chain-growth polymerization or addition polymerization that involves the polymerization of monomers initiated with anions. The type of reaction has many manifestations, but traditionally vinyl monomers are used.