As shown by the adhesion between the solid surface and the liquid surface, the molecules on the solid surface have a certain surface energy. When it comes into contact with the gas, it can attract some gas molecules to the solid surface to reduce its surface energy. This phenomenon is called adsorption.
The adsorption phenomenon can be divided into physical adsorption and chemical adsorption. Physical adsorption is caused by the gravitational force between the solid surface molecules and the adsorbed gas molecules. Chemical adsorption is caused by the chemical bond energy of the solid surface molecules. For a certain solid, it often only has chemical adsorption on certain gas molecules (depending on the molecular structure), thus showing the selectivity of adsorption.
Physical adsorption and chemical adsorption often act at the same time. The speed of physical adsorption is very fast, so it is easy to reach equilibrium, while the speed of chemical adsorption is slow. When the temperature rises, the thermal motion of gas molecules intensifies, which will reduce the physical adsorption capacity and accelerate the speed of chemical adsorption. Therefore, at room temperature, it is mainly physical adsorption, while at high temperature, the chemical adsorption effect is significant.
The adsorption phenomenon is widely used in industry and daily life, such as solid catalysts for chemical reactions, which mostly rely on adsorption activation to catalyze, and adsorbents in gas masks selectively adsorb harmful gases.
