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title: "A student places \\(10.0\\text{ g}\\) of solid ammonium nitrate, \\(\\text{NH}_4\\text{NO}_3(s)\\), into \\(100.0\\text{ g}\\) of distilled water at \\(22.0\\ ^\\circ\\text{C}\\) inside a well-insulated coffee-cup calorimeter. The mixture is stirred until the solid completely dissolves, and the final temperature of the solution is recorded as \\(15.5\\ ^\\circ\\text{C}\\). Assuming negligible heat exchange with the calorimeter walls and the air, which of the following correctly classifies the dissolution process and describes the transfer of thermal energy?"
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url: "https://nerd-notes.com/ubq/119678/"
date_modified: "2026-08-21T08:12:02+00:00"
---

# A student places \(10.0\text{ g}\) of solid ammonium nitrate, \(\text{NH}_4\text{NO}_3(s)\), into \(100.0\text{ g}\) of distilled water at \(22.0\ ^\circ\text{C}\) inside a well-insulated coffee-cup calorimeter. The mixture is stirred until the solid completely dissolves, and the final temperature of the solution is recorded as \(15.5\ ^\circ\text{C}\). Assuming negligible heat exchange with the calorimeter walls and the air, which of the following correctly classifies the dissolution process and describes the transfer of thermal energy?

A student places \(10.0\text{ g}\) of solid ammonium nitrate, \(\text{NH}_4\text{NO}_3(s)\), into \(100.0\text{ g}\) of distilled water at \(22.0\ ^\circ\text{C}\) inside a well-insulated coffee-cup calorimeter. The mixture is stirred until the solid completely dissolves, and the final temperature of the solution is recorded as \(15.5\ ^\circ\text{C}\). Assuming negligible heat exchange with the calorimeter walls and the air, which of the following correctly classifies the dissolution process and describes the transfer of thermal energy?

- **A.** The process is exothermic (\(\Delta H_{\text{soln}} < 0\)) because thermal energy is transferred from the water to the thermometer as the solid dissolves.
- **B.** The process is exothermic (\(\Delta H_{\text{soln}} < 0\)) because the energy released during ion hydration is greater in magnitude than the lattice energy required to separate the ions.
- **C.** The process is endothermic (\(\Delta H_{\text{soln}} > 0\)) because the dissolving solute absorbs thermal energy from the water, decreasing the average kinetic energy of the solvent molecules.
- **D.** The process is endothermic (\(\Delta H_{\text{soln}} > 0\)) because thermal energy is released from the solute into the surroundings as ionic bonds within the crystal lattice are broken.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119678/*