Dissolving ammonium nitrate in water is endothermic; what observable temperature change occurs?

• A. The dissolution absorbs heat, so the solution temperature decreases.
• B. The dissolution releases heat, so the solution temperature increases.
• C. The dissolution produces no temperature change.
• D. The dissolution first decreases then increases temperature.

Answer: (A)

When a process absorbs heat from its surroundings, the temperature of the surroundings (in this case, the water and solution) drops. Dissolving ammonium nitrate in water is endothermic, so heat is drawn from the water to drive the dissolution. The net effect is a cooling of the solution as energy moves into the dissolving system. You’d observe the solution getting colder as it dissolves.

If heat were released, the temperature would rise; if there were no net heat transfer, the temperature would stay the same. Since ammonium nitrate dissolves with heat absorption, the observable change is a decrease in temperature.