Chemisorption

Definition

Chemisorption is a type of adsorption where a molecule forms a strong chemical bond with a solid surface. This process is characterized by a significant energy change and involves the formation of covalent or ionic bonds between the adsorbate and the substrate, leading to a more stable attachment compared to physisorption. Understanding chemisorption is crucial as it plays a key role in various applications, including catalysis, sensor design, and surface chemistry.

5 Must Know Facts For Your Next Test

1. Chemisorption typically involves higher energies compared to physisorption, with bond energies often exceeding 50 kJ/mol.
2. The process can be irreversible, meaning that once molecules are chemisorbed, they may not desorb easily from the surface.
3. Temperature and pressure significantly influence the rate of chemisorption, with higher temperatures generally increasing the kinetic energy of molecules and enhancing interaction likelihood.
4. Chemisorption is essential in heterogeneous catalysis, where reactants must be chemisorbed onto catalyst surfaces to facilitate chemical reactions.
5. Surface coverage by adsorbates during chemisorption can lead to distinct changes in the physical and chemical properties of materials, impacting their functionality.

Review Questions

• How does chemisorption differ from physisorption in terms of bond strength and reversibility?
  • Chemisorption differs from physisorption primarily in the strength of the bond formed and its reversibility. Chemisorption involves the formation of strong chemical bonds, such as covalent or ionic bonds, leading to a more stable attachment. In contrast, physisorption relies on weak van der Waals forces, making it reversible. The strong nature of chemisorption often results in irreversible attachment of molecules to surfaces.
• Discuss the role of chemisorption in catalytic processes and why it is critical for enhancing reaction rates.
  • Chemisorption plays a vital role in catalytic processes as it enables reactant molecules to adhere to catalyst surfaces. This attachment allows for effective interaction between reactants and active sites on the catalyst, facilitating the transformation into products. The formation of strong bonds during chemisorption lowers the activation energy needed for the reaction to proceed, significantly enhancing reaction rates compared to uncatalyzed reactions.
• Evaluate how temperature and pressure affect chemisorption and relate this to practical applications such as sensor technology.
  • Temperature and pressure have profound effects on chemisorption rates and efficiency. Higher temperatures can increase molecular kinetic energy, enhancing the likelihood of reactant molecules achieving sufficient energy to overcome barriers for chemisorption. Similarly, increased pressure can drive more molecules toward surfaces, promoting higher rates of adsorption. In sensor technology, these principles are applied to design devices that rely on the selective chemisorption of target molecules on sensor surfaces, allowing for sensitive detection and measurement.

Related terms

Physisorption:

A weak form of adsorption where molecules adhere to a surface through van der Waals forces without forming any chemical bonds.

Catalysis: The process of accelerating a chemical reaction by using a substance called a catalyst, which often relies on chemisorption to facilitate reactant interactions.

Adsorption Isotherm: A model that describes how the quantity of adsorbate on a solid surface varies with pressure or concentration at constant temperature, relevant for understanding both chemisorption and physisorption.