Physical absorption – reversibility and thermal effect Which statement best characterizes physical (non-reactive) gas absorption into a liquid under typical conditions?

Introduction / Context:
Physical absorption describes the dissolution of a gas into a liquid without chemical reaction. Understanding its thermodynamic character and heat effects is crucial for absorber design, since both equilibrium and heat release influence column sizing and energy balances.

Given Data / Assumptions:

• No chemical reaction (solubility governed by Henry’s law).
• Isothermal assumptions are approximate; heats of solution exist.
• Desorption is possible by reducing partial pressure or raising temperature.

Concept / Approach:
Physical absorption is fundamentally reversible: the dissolved gas can be stripped by lowering its partial pressure or increasing temperature (Le Châtelier-type response). Most gas dissolution processes are mildly exothermic due to solvent–solute interactions, so a finite heat of solution is released. While far smaller than chemisorption heats, this heat can warm the solvent and reduce solubility, affecting performance if not removed by cooling.

Step-by-Step Solution:

Verification / Alternative check:
Plant data show absorber temperature bulges; cooling reduces solvent temperature and restores capacity, consistent with exothermic absorption and reversibility via partial-pressure changes.

Why Other Options Are Wrong:

• Irreversible: Contradicts common stripping and solvent regeneration practice.
• Only reversible or only exothermic: Incomplete description.

Common Pitfalls:
Neglecting heat effects (assuming isothermal operation) can underpredict column height since warm solvent holds less solute at the same partial pressure.

Final Answer:
both (b) and (c)