---
title: "A student evaluates ammonium nitrate, \\(\\text{NH}_4\\text{NO}_3\\), for use in an instant cold pack by dissolving a known amount of the solid in water. The dissolution is endothermic. Initially, the water, solid, and room are at the same temperature. The student performs the experiment in a covered, thin-walled vessel without an insulating jacket and calculates the enthalpy of dissolution using  \\[q_{\\text{solution}}=m_{\\text{solution}}c_{\\text{solution}}(T_f-T_i)\\]  and  \\[\\Delta H_{\\text{soln}}=-\\dfrac{q_{\\text{solution}}}{n_{\\text{NH}_4\\text{NO}_3}}\\]  Assume that heat exchange with the room is the only significant source of error. Compared with the accepted positive value of \\(\\Delta H_{\\text{soln}}\\), how will the calculated value be affected, and why?"
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url: "https://nerd-notes.com/ubq/119478/"
date_modified: "2026-08-19T12:40:37+00:00"
---

# A student evaluates ammonium nitrate, \(\text{NH}_4\text{NO}_3\), for use in an instant cold pack by dissolving a known amount of the solid in water. The dissolution is endothermic. Initially, the water, solid, and room are at the same temperature. The student performs the experiment in a covered, thin-walled vessel without an insulating jacket and calculates the enthalpy of dissolution using

\[q_{\text{solution}}=m_{\text{solution}}c_{\text{solution}}(T_f-T_i)\]

and

\[\Delta H_{\text{soln}}=-\dfrac{q_{\text{solution}}}{n_{\text{NH}_4\text{NO}_3}}\]

Assume that heat exchange with the room is the only significant source of error. Compared with the accepted positive value of \(\Delta H_{\text{soln}}\), how will the calculated value be affected, and why?

A student evaluates ammonium nitrate, \(\text{NH}_4\text{NO}_3\), for use in an instant cold pack by dissolving a known amount of the solid in water. The dissolution is endothermic. Initially, the water, solid, and room are at the same temperature. The student performs the experiment in a covered, thin-walled vessel without an insulating jacket and calculates the enthalpy of dissolution using

\[q_{\text{solution}}=m_{\text{solution}}c_{\text{solution}}(T_f-T_i)\]

and

\[\Delta H_{\text{soln}}=-\dfrac{q_{\text{solution}}}{n_{\text{NH}_4\text{NO}_3}}\]

Assume that heat exchange with the room is the only significant source of error. Compared with the accepted positive value of \(\Delta H_{\text{soln}}\), how will the calculated value be affected, and why?

- **A.** It will be too high, because thermal energy entering from the room makes \(T_f-T_i\) more negative.
- **B.** It will be too high, because the calculation counts thermal energy entering from the room as energy absorbed by the dissolution.
- **C.** It will be too low, because some thermal energy released by the dissolution is transferred from the solution to the room.
- **D.** It will be too low, because thermal energy enters the colder solution from the room, reducing the magnitude of the measured temperature decrease.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/119478/*