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MCQEasyJEE 2025Internal Energy & Enthalpy

JEE Chemistry 2025 Question with Solution

Which of the following mixing of 1 M1 \, \text{M} base and 1 M1 \, \text{M} acid leads to the largest increase in temperature?

  • A

    30 mL30 \, \text{mL} CH3COOHCH_3COOH and 30 mL30 \, \text{mL} NaOH

  • B

    45 mL45 \, \text{mL} CH3COOHCH_3COOH and 25 mL25 \, \text{mL} NaOH

  • C

    50 mL50 \, \text{mL} HCl and 20 mL20 \, \text{mL} NaOH

  • D

    30 mL30 \, \text{mL} HCl and 30 mL30 \, \text{mL} NaOH

Answer

Correct answer:C

Step-by-step solution

Standard Method

Given: All solutions are 1 M1 \, \text{M}. We must identify which mixing gives the largest increase in temperature.

Find: The option that produces the maximum heat on neutralization, hence the maximum rise in temperature.

Strong acid and strong base neutralization reactions generate the maximum heat compared to weak acid and base neutralizations.

From the provided solution, the comparison is made on the basis that the mix of 50 mL50 \, \text{mL} HCl and 20 mL20 \, \text{mL} NaOH involves a strong acid and a strong base and is stated to give the largest heat increase.

Therefore, the correct option is C.

Stepwise Extraction from the solution

Given:

  • Acid–base neutralization releases heat.
  • All acid and base solutions are 1 M1 \, \text{M}.

Find: Which mixture leads to the largest increase in temperature.

The extracted solution states the neutralization process as

Acid+Base→Salt+Water\text{Acid} + \text{Base} \rightarrow \text{Salt} + \text{Water}

and says that strong acid–strong base combinations generate maximum heat compared to weak acid neutralizations.

It further concludes that among the listed options, 50 mL50 \, \text{mL} HCl and 20 mL20 \, \text{mL} NaOH gives the highest heat increase.

Conclusion: The correct option is C.

Note: The source solution compares options qualitatively and concludes option C from the strong acid–strong base consideration.

Common mistakes

  • Assuming that a weak acid and strong base mixture will always release as much heat as a strong acid and strong base mixture is incorrect. Weak acids are not fully ionized, so the effective heat of neutralization is lower. Compare the acid strength before choosing the option.

  • Comparing only the total mixed volume can be misleading. A larger total volume does not automatically mean the largest temperature rise. First identify the nature of the acid and base, then compare the reacting amounts.

  • Treating all neutralization reactions as identical is wrong. CH3COOHCH_3COOH is a weak acid, whereas HCl is a strong acid. Use the fact that strong acid–strong base neutralization is more exothermic than weak acid–strong base neutralization.

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