Question

The adsorption of gases on metal surfaces is called (a) catalysis (b) occlusion (c) adsorption (d) absorption

Short answer

The correct answer is (c) Adsorption.

Step-by-step solution

Understanding the Terms

Start by understanding the terms: Catalysis is a process that increases the rate of a chemical reaction by adding a substance, the catalyst. Occlusion is a process where a material absorbs or adsorbs a gas into it. Adsorption is the process of particles (here gas) accumulating on a surface (in this case, metal), and absorption is when one substance is absorbed or incorporated into another.

Identify the Correct Term

Among these terms, the one that specifically describes the process of gases adhering to metal surfaces, that is, particles (here gas) accumulating on a surface (in this case, metal), is called 'adsorption'. So, 'adsorption' is the correct term.

Key concepts

Catalysis

Catalysis is a pivotal concept in chemistry that involves the acceleration of a chemical reaction by adding a substance known as a catalyst. Catalysts are not consumed during the reaction; they provide an alternative pathway for the reaction with a lower activation energy. In ordinary language, you can think of it as a facilitator that helps things along without getting used up in the process.

For instance, in the industrial synthesis of ammonia through the Haber process, iron is used as a catalyst to speed up the reaction between nitrogen and hydrogen gases. Students often confuse catalysis with the reactants or products themselves, but it's important to remember that catalysts are separate entities that only aid in the efficiency and speed of reactions.

Occlusion

Occlusion, in the context of chemistry, refers to the trapping of one substance within another. While the term might seem complicated, think of it like a sponge soaking up water. The water becomes entrapped in the network of the sponge's pores. However, unlike absorption, occlusion often implies that the trapped substance is not uniformly distributed within the host material.

For example, hydrogen can be occluded within metals such as palladium. This means that the metal has a structure that allows hydrogen to be held within it, creating a metal-hydride compound. Knowing the difference between occlusion and similar processes like adsorption or absorption is crucial for students to accurately describe the interaction of substances at the molecular level.

Chemical Reaction

A chemical reaction is a process where substances, known as reactants, transform into different substances, called products. This transformation involves the breaking and forming of chemical bonds, leading to changes in the composition of matter.

An easy example of a chemical reaction is the combustion of methane in the presence of oxygen to produce carbon dioxide and water. This process releases energy in the form of heat and light. Students should remember that each chemical reaction is governed by the laws of conservation of mass and energy, meaning that in a closed system, mass and energy are neither created nor destroyed, only transferred or transformed.

Absorption

Absorption is often confused with adsorption, but the two are distinct processes. Absorption involves the uptake of a substance into the bulk, or volume, of another material. Imagine a sponge absorbing water— the water is not just on the surface; it permeates throughout the sponge's entire volume.

A classic example of absorption is when water is absorbed by a towel. The water molecules move into the spaces between the fibers of the towel, spreading throughout the material. It's important for students to understand this concept clearly as it is a fundamental mechanism in many biological and chemical processes.