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NEET CHEMISTRYThermodynamicsEasy

Question

The heat of neutralisation of a strong acid and a strong alkali is 57.0 kJ mol−157.0 \text{ kJ mol}^{-1}. The heat released when 0.5 mole of HNO30.5 \text{ mole of } HNO_{3} solution is mixed with 0.2 mole of KOH0.2 \text{ mole of } KOH is [KCET 1991; AIIMS 2002]:

A

57.0 kJ

B

11.4 kJ

C

28.5 kJ

D

34.9 kJ

Step-by-Step Solution

The enthalpy of neutralisation is defined as the heat change accompanying the reaction of one mole of H+H^{+} ions from an acid with one mole of OH−OH^{-} ions from a base to form one mole of water. For strong acids and strong bases, this value is constant at approximately −57.3 kJ mol−1-57.3 \text{ kJ mol}^{-1} (given here as 57.0 kJ mol−157.0 \text{ kJ mol}^{-1}).

In the reaction between HNO3HNO_{3} and KOHKOH (HNO3+KOH→KNO3+H2OHNO_{3} + KOH \rightarrow KNO_{3} + H_{2}O), both are strong electrolytes .

  1. Identify the moles of reactants: We have 0.5 mol0.5 \text{ mol} of H+H^{+} (from HNO3HNO_{3}) and 0.2 mol0.2 \text{ mol} of OH−OH^{-} (from KOHKOH).
  2. Identify the limiting reagent: According to the sources, the reactant present in the least stoichiometric amount is the limiting reagent . Here, KOHKOH (0.2 mol0.2 \text{ mol}) is the limiting reagent.
  3. Calculate heat released: The amount of water formed is limited by the KOHKOH, resulting in 0.2 mol0.2 \text{ mol} of H2OH_{2}O. Heat released = (moles of water formed) ×\times (heat of neutralisation per mole) Heat released = 0.2 mol×57.0 kJ/mol=11.4 kJ0.2 \text{ mol} \times 57.0 \text{ kJ/mol} = 11.4 \text{ kJ}.

Thus, the total heat evolved is 11.4 kJ11.4 \text{ kJ}, which matches Option B.

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.

CHEMISTRYThermodynamicsneutralisationstrongstrongalkalireleased

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