Gas solubility trend: at fixed pressure, how does the solubility of ammonia in water change as temperature increases?

Introduction / Context:Gas solubility in liquids is central to absorber design, stripping, and environmental control. Most gases, including ammonia, become less soluble as temperature rises at a fixed pressure, because dissolution is often exothermic and higher temperature favors desorption according to Le Châtelier’s principle.

Given Data / Assumptions:

• Liquid solvent: water; solute gas: ammonia (NH3).
• Pressure held constant (e.g., near 1 atm).
• Equilibrium solubility is considered (not kinetic absorption rates).

Concept / Approach:Henry’s law constants typically increase with temperature for gases like NH3, meaning a higher gas-phase partial pressure is required to achieve the same dissolved concentration as T rises. Equivalently, at fixed partial pressure, the equilibrium dissolved concentration decreases as temperature increases. This underpins operating choices in gas strippers where heating the solution helps remove dissolved ammonia.

Step-by-Step Solution:

Verification / Alternative check:Data tables for NH3 solubility in water show strong decline with temperature, a practical concern in wastewater treatment and scrubber design.

Why Other Options Are Wrong:

• (a) and (d) contradict empirical data.
• (c) ignores temperature dependence.
• (e) has no physical basis here.

Common Pitfalls:Confusing highly soluble gases like NH3 with atypical systems; even for NH3, the general trend of decreasing solubility with higher temperature holds.

Final Answer:decreases