Question

"It is only the absorbed light radiations that are effective in producing a chemical reactions." This is the statement of (a) Lambert law (b) Lambert-Beer law (c) Grotthus-Draper law (d) Stark-Einstein law

Short answer

The correct answer is Grotthus-Draper law.

Step-by-step solution

Identify the law

Firstly, evaluate the statement, 'It is only the absorbed light radiations that are effective in producing chemical reactions.' This statement suggests that for a chemical reaction to occur, light radiation must be absorbed. This is a fundamental concept of one particular law in physics and chemistry, which states that only absorbed light can cause a chemical reaction.

Check each option

Secondly, compare the statement to each law: \n- Lambert law is related to the intensity of light falling upon a surface decreasing exponentially with the thickness of the absorbed material, which does not align with our statement. \n- Lambert-Beer law describes how the absorption of light by a substance is directly proportional to its concentration, which again is not closely related to our statement. \n- Grotthus-Draper law, also known as the Principle of Photochemical Activation, states exactly this concept: that only the light that is absorbed by a system can bring about a photochemical change. \n- Stark-Einstein law is about the photon emission and absorption processes, which is not directly related to the statement.

Select correct law

After comparing the options, it is clear that the statement aligns most closely with Grotthus-Draper law. Therefore, the correct answer is Grotthus-Draper law.

Key concepts

Grotthus-Draper law

The Grotthus-Draper Law is foundational in the field of photochemistry. This law, formulated by Théodor Grotthus and John Draper in the early 19th century, highlights the importance of light absorption in chemical reactions. Simply put, it states that only the light absorbed by a substance can be effective in initiating a chemical transformation. This means that if light passes through a substance without being absorbed, it will not contribute to a photochemical change. Understanding this concept helps in designing experiments and interpreting results in photochemical reactions.

In practical terms, this means:

• Light must be absorbed to initiate changes.
• Unabsorbed light has no impact on the reaction.
• Optimizing the reaction conditions often involves ensuring proper absorption.

By recognizing which wavelengths are absorbed by a substance, scientists can predict and manipulate reactions.

Absorption of light

Absorption of light is a critical process in photochemistry and refers to the way light energy is taken in by molecules. When a molecule absorbs light, it gains energy, leading to an excited state that can then participate in chemical reactions. Without absorption, no changes would occur, as noted by the Grotthus-Draper Law.

Things to remember about light absorption include:

• The amount of light absorbed is dependent on the wavelength of the light and the properties of the molecule.
• Molecules have specific wavelengths they absorb, known as their absorption spectrum.
• The transition to an excited state can cause bonds to rearrange, facilitating chemical reactions.

This process is fundamental in areas such as photosynthesis, where light absorption by chlorophyll is key to energy conversion.

Chemical reactions

Chemical reactions are processes where molecules interact to form new products. In the context of photochemistry, these reactions are driven by the energy absorbed from light. When light is absorbed, it provides the energy needed to break bonds, form new ones, or alter structures, enabling new chemical species to form.

Key aspects of photochemical reactions include:

• An initial absorption of photons leading to an excited state.
• Potential changes in chemical reactivity due to the excited state.
• Possibility of forming radicals or other reactive species that wouldn't occur in the absence of light.

Such reactions are ubiquitous in nature and technology—from the synthesis of vitamin D in our skin to the design of light-sensitive materials in solar panels. By understanding the role of light in chemical reactions, scientists can harness solar energy and design innovative solutions to real-world problems.