Q31
jee_main_2025_24_jan_evening
Enthalpy of Neutralization
Which of the following mixing of 1M base and 1M acid leads to the largest increase in temperature?
Solution
### Related Formula
Q = n_textreacted cdot Delta H_textneutralization
Delta T = fracQm cdot c
### Core Logic
The temperature rise depends directly on the total heat released (Q) normalized by the total heat capacity of the resulting mixed volume (m cdot c). Let's evaluate the millimoles of mathrmH^+ and mathrmOH^- that react in each mixture:
1. **Option 1:** 30text mL of 1mathrmM mathrmHCl + 30text mL of 1mathrmM mathrmNaOH
textReactive millimoles = 30text mmol. Both are strong electrolytes, releasing full neutralization energy (sim -57.3text kJ/mol).
Total volume = 60text mL.
2. **Option 2:** 30text mL of 1mathrmM mathrmCH_3COOH + 30text mL of 1mathrmM mathrmNaOH
textReactive millimoles = 30text mmol. However, since acetic acid is a weak acid, part of the heat is consumed in its ionization. Thus, less total heat is evolved compared to Option 1.
3. **Option 3:** 50text mL of 1mathrmM mathrmHCl + 20text mL of 1mathrmM mathrmNaOH
textLimiting reagent = mathrmNaOH = 20text mmol. Only 20text mmol reacts.
Total volume = 70text mL.
4. **Option 4:** 45text mL of 1mathrmM mathrmCH_3COOH + 25text mL of 1mathrmM mathrmNaOH
textLimiting reagent = 25text mmol weak neutralization profile.
Comparing Option 1 and Option 3, Option 1 releases significantly more heat (30text mmol vs 20text mmol) into a smaller volume (60text mL vs 70text mL), yielding the largest increase in temperature Delta T.
### Pattern Recognition
To maximize Delta T, look for the option that maximizes the amount of reacting strong acid and strong base equivalents while keeping the total solution volume as small as possible.
### Evaluation Rubric / Model Answer
null
### Chapter Mix
Class 11 Chemistry: Thermodynamics
Class 11 Chemistry: Equilibrium
