# Explain why dissolving ammonium nitrate, NH₄NO₃(s), in water produces a solution that feels cold to the touch, and state what this indicates about the sign of ΔH for the dissolving process.

> IB DP Chemistry Standard Level (2023 syllabus) — R1.1 Measuring enthalpy changes · Explain · 4 marks

> When ammonium nitrate is dissolved in water, the mixture becomes noticeably cold. This property is exploited in instant cold packs used in sports medicine.

## Mark scheme (4 marks)

1. The dissolving process is endothermic, meaning energy is absorbed FROM the surroundings (the water/solution) BY the system.
2. Energy is taken from the water/solution, reducing the thermal energy (temperature) of the surroundings, which is why the solution feels cold.
3. The energy required to break apart the ionic lattice (lattice enthalpy) exceeds the energy released when ions are hydrated (hydration enthalpy), giving an overall energy input.
4. ΔH for the dissolving process is positive (ΔH > 0).

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- [Revision notes for IB DP Chemistry Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
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