Allowed or forbidden reactions

In summary, The reaction described involves the conversion of a proton and a neutron into a lambda particle and a positive sigma particle. It is allowed due to the conservation of charge and baryon number, but not conservation of strangeness or the third component of isospin. This makes it a weak allowed reaction, although the cross section is expected to be very small due to the changes in strangeness. The reaction is not considered a typical weak reaction due to the lack of conservation of strangeness and the third component of isospin.
  • #1
Aleolomorfo
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Homework Statement
Establish whether the following reactions are allowed or not, if it is not, give the reasons
Relevant Equations
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Hello everybody!

I have a doubt about a reaction.

$$ p + n \rightarrow \Lambda + \Sigma^+ $$

I have to establish if it is allowed or not.
  • Charge is conserved (1 -> 1)
  • Baryon number is conserved (2 -> 2)
  • Strangeness is not conserved (0 -> -2)
  • Third component of the isospin is not conserved (0 -> 1)
  • Isospin is conserved (1 or 0 -> 1)
  • Angular momentum is conserved (1 or 0 -> 1 or 0)
Since strangeness and the third component of the isospin are not conserved, it is not a strong reaction, and neither an electromagnetic one since the third component of the isospin is not conserved.

My conclusion is that this is a weak allowed reaction. I would like to know if it is correct, because this is not exactly a "typical" weak reaction.

Thanks in advance!
 
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  • #2
It is technically allowed but the cross section must be tiny with the strangeness changing by two.
 
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1. What is an allowed reaction?

An allowed reaction is a chemical reaction that is energetically favorable and proceeds spontaneously without the input of external energy. This means that the products of the reaction have a lower energy state than the reactants, resulting in a release of energy.

2. How do you determine if a reaction is allowed?

The thermodynamic laws of thermodynamics can be used to determine whether a reaction is allowed or not. If the reaction has a negative Gibbs free energy (ΔG) value, it is considered energetically favorable and therefore allowed. Additionally, the entropy (ΔS) and enthalpy (ΔH) values of the reaction can also be used to determine its feasibility.

3. What factors can affect whether a reaction is allowed or forbidden?

The energy difference between the reactants and products, the temperature, and the concentration of reactants can all affect whether a reaction is allowed or not. In some cases, the presence of a catalyst can also change the thermodynamics of a reaction and make it allowed.

4. Can a forbidden reaction ever occur?

In certain cases, a forbidden reaction can occur if it is coupled with an energetically favorable reaction. This means that the energy released from the allowed reaction can drive the otherwise forbidden reaction and make it occur. However, in most cases, a forbidden reaction will not occur without the input of external energy.

5. How can you control whether a reaction is allowed or forbidden?

The thermodynamics of a reaction cannot be controlled, but the rate of a reaction can be controlled through various factors such as temperature, concentration, and the use of a catalyst. By manipulating these factors, the rate of an allowed or forbidden reaction can be altered. Additionally, the use of external energy such as heat or light can also drive a reaction and make it occur.

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