Question

At low pressure, the amount of the gas adsorbed is ____ proportional to the pressure. (a) directly (b) inversely (c) sometimes directly, sometimes inversely (d) none of these

Short answer

The correct answer is (a) directly.

Step-by-step solution

Understand Adsorption

Adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface. This process creates a film of the adsorbate (the molecules or atoms being accumulated) on the surface of the adsorbent. It differs from absorption, where a substance diffuses into a liquid or solid to form a solution.

Apply Basic Gas Laws

Adsorption is directly proportional to the pressure of the gas. This is because as the pressure of a gas increases, more molecules or atoms of the gas are in the immediate vicinity of the adsorbent's surface. Hence, more gas molecules or atoms are accumulating on the surface, leading to a higher rate of adsorption.

Relate to Low Pressure

The direct relationship between pressure and adsorption holds true at low pressures. Therefore, the more the pressure, the more the amount of a gas gets adsorbed.

Key concepts

Understanding Physical Chemistry

Physical chemistry delves into the internal workings of molecules and how they interact through chemical reactions. Understanding the principles of adsorption—the accumulation of particles on a surface—necessitates a deep dive into physical chemistry. This field blends the laws of physics with chemical processes to explain phenomena on an atomic and molecular level.

When focusing on adsorption, we're dealing with atomic or molecular attraction and how different pressures can influence the amount of gas adhering to a surface. High-school and introductory university courses often touch on this within general studies of physical chemistry. By looking at adsorption, students can explore how their environment at the microscopic level is governed by principles such as energy states, entropy, and enthalpy, which are fundamental concepts in physical chemistry.

Exploring Surface Chemistry

Surface chemistry provides valuable insights into the matter that occupies the threshold between two phases, like a gas and a solid. The properties of this surface—an adsorbent—can greatly affect the adsorption process. Factors that affect adsorption include temperature, the nature of the adsorbent and adsorbate, and the pressure conditions of the gas involved.

Interplay of Pressure and Adsorption

At a low pressure, adsorption is directly proportional to the pressure because an increase in gas pressure will lead to more gas molecules coming into contact with the adsorbent's surface. In the context of surface chemistry, studying how adsorption varies with pressure allows students to predict and manipulate how substances interact at surfaces—information that's critical in various industrial processes, such as catalysis and purification methods.

Gas Laws Connection

Gas laws afford a predictive power over the behavior of gases under different conditions of pressure, temperature, and volume. Fundamentally, Boyle's Law states that pressure is inversely proportional to volume for a fixed amount of gas at constant temperature, while Charles's Law demonstrates that volume is directly proportional to temperature.

Seeing adsorption through the lens of gas laws, it becomes evident why at low pressures the amount of gas adsorbed increases with pressure—a relation that mirrors the direct proportionality of volume to pressure as seen in Amontons's Law (also known as Gay-Lussac's Law) of pressure and temperature at constant volume. Understanding these laws helps students to comprehend why more gas is adsorbed with increasing pressure, as witnessed in the step by step solution of the exercise on adsorption.