Question

Chemisorption generally ____ with temperature. (a) increases (b) decreases (c) remains the same (d) none of these

Short answer

(a) Increases

Step-by-step solution

Understanding Concept

First, a comprehension of the chemisorption process is needed. This process involves the formation of a chemical bond, hence requiring activation energy. As we know, most chemical reactions usually need heat to be supplied for the reaction to occur.

Connect Concept with Temperature

In the second step, connect the chemisorption concept with temperature. As temperature increases, the molecules will have more kinetic energy, this means they are more likely to overcome the activation energy barrier, leading to chemisorption.

Conclusion

Therefore, chemisorption generally increases as temperature rises, because more molecules are likely to overcome the activation energy barrier required for the process. Thus, the correct answer to the problem is (a) increases.

Key concepts

Activation Energy in Chemisorption

The concept of activation energy is central to understanding chemisorption. Activation energy is the minimum energy barrier that must be overcome for a chemical reaction to occur. In the context of chemisorption, molecules must possess enough kinetic energy to disrupt the existing bonds and form new ones with the surface of the material.

Since chemisorption involves forming chemical bonds, which is an activation energy-requiring process, it's essential to consider this energy threshold when predicting if and how quickly chemisorption will occur. An increase in temperature generally provides the energy needed for more molecules to reach or surpass this activation energy, thereby increasing the rate and extent of chemisorption.

Temperature Dependence of Chemisorption

Temperature plays a pivotal role in the process of chemisorption due to its impact on molecules' kinetic energy. As a rule of thumb, chemical reactions—including the formation of chemisorbed layers—tend to increase in rate as the temperature rises.

This occurs because molecules move faster and collide more energetically at higher temperatures, leading to a higher probability of overcoming the activation energy. Consequently, chemisorption generally increases with temperature, as more adsorbate species acquire the necessary energy to form a bond with the substrate.

However, it is crucial to note that while an increase in temperature initially promotes chemisorption, there's a limit. At very high temperatures, desorption may occur as the adsorbed species gain enough energy to break the bonds and release from the surface.

Chemical Bond Formation in Chemisorption

Chemisorption is characterized by the formation of strong chemical bonds between the adsorbate and the surface, which distinguishes it from physisorption—a process involving weaker van der Waals forces. Unlike physisorption, chemisorption bonds are similar in strength to typical covalent or ionic bonds.

The formation of these chemical bonds requires a specific orientation and adequate energy to allow for the sharing or transfer of electrons. This selectivity in orientation and requirement for energy contribute to the overall specificity and stability of chemisorption. Additionally, the chemical bond formation in chemisorption is typically a one-layer phenomenon because the energy and specificity decrease considerably beyond the first layer of adsorbed molecules.