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In nuclear physics and nuclear chemistry, a nuclear reaction is a process in which two nuclei, or a nucleus and an external subatomic particle, collide to produce one or more new nuclides. Thus, a nuclear reaction must cause a transformation of at least one nuclide to another.
The following apply for the nuclear reaction: a + b ↔ R → c in the centre of mass frame , where a and b are the initial species about to collide, c is the final species, and R is the resonant state .
In the absence of a nuclear reaction the number of atoms flowing in and out must remain the same, even in the presence of a chemical reaction. For a balance to be formed, the boundaries of the system must be clearly defined. Mass balances can be taken over physical systems at multiple scales.
A reaction with a negative Q value is endothermic, i.e. requires a net energy input, since the kinetic energy of the final state is less than the kinetic energy of the initial state. [1] Observe that a chemical reaction is exothermic when it has a negative enthalpy of reaction, in contrast a positive Q value in a nuclear reaction.
Thus they again take their places in the chain: plutonium-239, used in nuclear weapons, is the major example, decaying to uranium-235 via alpha emission with a half-life 24,500 years. There has also been large-scale production of neptunium-237, which has resurrected the hitherto extinct fourth chain. [ 7 ]
If a reaction network has n reactions and m participating molecular species, then the stoichiometry matrix will have correspondingly m rows and n columns. For example, consider the system of reactions shown below: S 1 → S 2 5 S 3 + S 2 → 4 S 3 + 2 S 2 S 3 → S 4 S 4 → S 5. This system comprises four reactions and five different molecular ...
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In the gas phase, the comproportionation reaction is much faster because of the much higher mobility of the reacting species as illustrated, e.g., in the Claus reaction where H 2 S and SO 2 react together to form elemental sulfur. Various classical comproportionation reactions are detailed in the series of examples here below.