Question

When $5\text{mL}$ of a $1.0\text{M}HCl$ solution is mixed with $5\text{mL}$ of a $0.1\text{M}NaOH$solution, temperature of solution increases by $t{}^{\circ }\text{C}$. Which of the following(s) can be predicted from this observation?

• A. $\text{If 5 mL of 0.1 M HCl is mixed with 5 mL 0.1 M}N{H}_3$
  $\text{solution, the temperature rise will be less than}t{}^{\circ }C$
• B. $\text{If 5 mL 0.1 M}C{H}_{3}COOH\text{is mixed with 5 mL 0.1 M NaOH,}$
  $\text{the temperature rise will be less than}t{}^{\circ }C$
• C. $\text{If 10 mL of 1.0 M HCl is mixed with 10 mL of 0.1 M NaOH,}$
  $\text{the temperature rise will be}2t{}^{\circ }C$
• D. $\text{If 10 mL of 0.1 M HCl is mixed with 10 mL of 0.1 M NaCl,}$
  $\text{the temperature rise will be}t{}^{\circ }C$

Answer 1

Answer: (A), (B)

$\text{If 5 mL 0.1 M}C{H}_{3}COOH\text{is mixed with 5 mL 0.1 M NaOH,}$

$\text{the temperature rise will be less than}t{}^{\circ }C$
Reaction proceeds by limiting reagent only.
Enthalpy of nuetralisation is the change in enthalpy that occurs when one equivalent of acid and base undergo neutralisation to form water and salt.
The enthalpy of neutralisation for between a strong acid and base is $-57.62\text{kJ/mol}$ at $25{}^{\circ }C$.
Enthalpy of neutralization decreases, when acid or base or both are weak.

a) Since ammonia is a weak base, the heat liberated and temperature rise will be less than $t{}^{\circ }C$.
b) Since acetic acid is a weak acid, the heat liberated and temperature rise will be less than $t{}^{\circ }C$.
c) Here the number of moles of acid and base are doubled. however since volume is also doubled, the rise in temperature will be same.
d) No heat will be liberated.