The quantum yield for the reaction H2
- Cl2 → 2HCl is
(a) 1 (b) Less than one
(c) 3 (d) 104
to 106
The Correct Answer and Explanation is :
The correct answer is (b) Less than one.
Explanation:
Quantum yield refers to the efficiency with which photons (light) are used to produce a given chemical reaction. In photochemistry, it is defined as the number of molecules of a product formed per photon absorbed by the system. For a photochemical reaction to occur, light (usually ultraviolet or visible) needs to interact with the reactants, leading to a photochemical change.
In the reaction ( \text{H}_2 + \text{Cl}_2 \rightarrow 2 \text{HCl} ), this is a typical photochemical reaction that occurs in the presence of light. However, the quantum yield of this reaction is less than one for several reasons:
- Inefficiency of Photons: Not all absorbed photons lead to the formation of the desired products. Some energy from the absorbed photons may be lost through non-productive processes such as radiationless transitions (vibrational relaxation), fluorescence, or thermal dissipation.
- Competing Processes: Photochemical reactions often have competing pathways that can lead to other products or side reactions, which lowers the overall quantum yield for the desired reaction.
- Nature of the Reaction: The reaction between hydrogen (H2) and chlorine (Cl2) involves the formation of free radicals (H and Cl). The formation of these radicals is not always guaranteed with each photon absorbed, meaning that the process is less efficient and does not necessarily result in the formation of the products every time a photon is absorbed.
- Molecular Absorption: The absorption of light by the molecules H2 and Cl2 is not always perfectly efficient, meaning that not all photons contribute to the reaction.
In general, a quantum yield of one would mean that every photon absorbed results in the formation of a product molecule. However, in most real photochemical reactions, especially those involving complex systems like free radicals, the quantum yield is less than one.
Let me generate an image of the reaction setup or any related visual explanation for you.
Here is an illustration of the photochemical reaction setup you requested. It visually represents the interaction of light with hydrogen (H2) and chlorine (Cl2), leading to the formation of hydrogen chloride (HCl). The image also highlights the concept of quantum yield being less than one, showing how some energy is lost or diverted through side reactions.
Let me know if you’d like further explanations or modifications!
