Which of the following compounds will absorb the maximum quantity of heat when dissolved in the same amount of

Question

Which of the following compounds will absorb the maximum quantity of heat when dissolved in the same amount of water? The heats of solution ($\Delta H_{sol}$) of these compounds at $25^{\circ}C$ in kJ/mol of each solute are given in brackets [AMU (Engg.) 2000]:

Accepted Answer

In thermodynamics, the sign of the enthalpy change ($\Delta H$) determines whether a process absorbs or releases energy.

1.  **Heat Absorption (Endothermic):** Processes that absorb heat from the surroundings have a **positive enthalpy change** ($\Delta H > 0$) .
2.  **Heat Evolution (Exothermic):** Processes that release heat to the surroundings have a **negative enthalpy change** ($\Delta H < 0$) .
3.  **Enthalpy of Solution ($\Delta_{sol}H$):** This is defined as the enthalpy change when one mole of a substance dissolves in a specified amount of solvent . For most ionic compounds, the dissolution process is endothermic .

Comparing the given heat of solution values:
*   **$HNO_{3}$ ($\Delta H = -33$):** Exothermic; releases heat.
*   **$KCl$ ($\Delta H = +17.64$):** Endothermic; absorbs heat.
*   **$NH_{4}NO_{3}$ ($\Delta H = +25.5$):** Endothermic; absorbs heat.
*   **$HCl$ ($\Delta H = -74.1$):** Exothermic; releases heat.

Since the question asks for the **maximum quantity of heat absorbed**, we look for the highest positive value. **$NH_{4}NO_{3}$** absorbs $25.5$ kJ of heat per mole, which is greater than the heat absorbed by $KCl$ ($17.64$ kJ/mol). Therefore, Option C is correct.

Step-by-Step Solution

Practice All CHEMISTRY Questions