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NEETChemistryThermodynamics (C)

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): Given H_f^ ( H ₂ O (l)) = -286 kJ mol ⁻¹ and H_f^ ( OH ^-(aq)) = -230 kJ mol ⁻¹ , the standard enthalpy of neutralization of a strong acid and strong base is -56 kJ mol ⁻¹ . Reason (R): The standard enthalpy of formation of H ^+(aq) is taken as zero by convention. In the light of the above statemen

Options

  1. ABoth Assertion and Reason are true but Reason is not the correct explanation of Assertion.
  2. BBoth Assertion and Reason are true and Reason is the correct explanation of Assertion.
  3. CAssertion is true but Reason is false.
  4. DAssertion is false but Reason is true.

Correct answer

B. Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Step-by-step solution

The net ionic equation for the neutralization of a strong acid and a strong base is: H ^+(aq) + OH ^-(aq) H ₂ O (l) The standard enthalpy of neutralization is calculated using Hess's Law: H_ neut ^ = H_f^ ( H ₂ O (l)) - [ H_f^ ( H ^+(aq)) + H_f^ ( OH ^-(aq))] By IUPAC convention, the standard enthalpy of formation of the aqueous hydrogen ion, H ^+(aq) , is assigned a value of zero at all temperatures. Thus, the Reason is true. Substituting the given values: H_ neut ^ = -286 - [0 + (-230)] = -286 + 230 = -56 kJ mol

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