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NEET CHEMISTRYThermodynamicsEasy

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 (ΔHsol\Delta H_{sol}) of these compounds at 25C25^{\circ}C in kJ/mol of each solute are given in brackets [AMU (Engg.) 2000]:

A

HNO3(ΔH=33)HNO_{3} (\Delta H = -33)

B

KCl(ΔH=+17.64)KCl (\Delta H = +17.64)

C

NH4NO3(ΔH=+25.5)NH_{4}NO_{3} (\Delta H = +25.5)

D

HCl(ΔH=74.1)HCl (\Delta H = -74.1)

Step-by-Step Solution

In thermodynamics, the sign of the enthalpy change (ΔH\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 (ΔH>0\Delta H > 0) .
  2. Heat Evolution (Exothermic): Processes that release heat to the surroundings have a negative enthalpy change (ΔH<0\Delta H < 0) .
  3. Enthalpy of Solution (ΔsolH\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:

  • HNO3HNO_{3} (ΔH=33\Delta H = -33): Exothermic; releases heat.
  • KClKCl (ΔH=+17.64\Delta H = +17.64): Endothermic; absorbs heat.
  • NH4NO3NH_{4}NO_{3} (ΔH=+25.5\Delta H = +25.5): Endothermic; absorbs heat.
  • HClHCl (ΔH=74.1\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. NH4NO3NH_{4}NO_{3} absorbs 25.525.5 kJ of heat per mole, which is greater than the heat absorbed by KClKCl (17.6417.64 kJ/mol). Therefore, Option C is correct.

Exam Context & Concepts Covered

This question aligns with the NEET CHEMISTRY syllabus, specifically targeting concepts from Thermodynamics. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

CHEMISTRYThermodynamicsfollowingcompoundsabsorbmaximumquantity

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