The change in enthalpy per unit weight of adsorbed gas when adsorbed on gas free or "outgassed" adsorbent to from a definite concentration of adsorbate is called its

ANS:A - integral heat of adsorption.

The integral heat of adsorption refers to the total amount of heat absorbed or released when a gas is adsorbed onto a solid surface to form a definite concentration of adsorbate. It represents the overall heat change associated with the adsorption process from the initial state, where the adsorbent surface is free of adsorbate (often referred to as the "outgassed" state), to the final state with a specific concentration of adsorbate molecules attached to the surface. Here's how the integral heat of adsorption is typically understood and measured:

1. Initial State (Outgassed Adsorbent): The adsorbent material, such as activated carbon or silica gel, is initially devoid of any adsorbate molecules. This state is often achieved by heating the adsorbent to remove any previously adsorbed species, ensuring a clean starting point for the adsorption experiment.
2. Adsorption Process: Gas molecules from the surrounding environment come into contact with the adsorbent surface and adhere to it due to intermolecular forces, such as Van der Waals forces or hydrogen bonding. As gas molecules accumulate on the surface, they form a monolayer or multilayer of adsorbate.
3. Final State (Definite Concentration of Adsorbate): At equilibrium, a specific concentration of adsorbate molecules is reached on the adsorbent surface. The integral heat of adsorption accounts for the total amount of heat absorbed or released during this process, including the heat required to break bonds between gas molecules and the heat released when new bonds are formed between gas molecules and the adsorbent surface.
4. Measurement: The integral heat of adsorption can be measured experimentally using techniques such as calorimetry. By monitoring the heat flow during the adsorption process, researchers can determine the total amount of heat exchanged between the adsorbent and the adsorbate.

Understanding the integral heat of adsorption is important in various applications, including gas separation processes, catalysis, and the design of adsorption-based technologies such as adsorption refrigeration systems. It provides valuable insights into the thermodynamic aspects of adsorption and helps optimize processes for practical applications.