Question

The amount of the heat released when $20ml$ $0.5M$ $NaOH$ is mixed with $100ml$ $0.1M$ $HCl$ is $x$ $kJ$. The heat of neutralization is:

• A. $-100x$ $kJ/mol$
• B. $-50x$ $kJ/mol$
• C. $+100x$ $kJ/mol$
• D. $+50x$ $kJ/mol$

Answer 1

The correct option is A $-100x$ $kJ/mol$

Millimoles (or milliequivalents) of $NaOH=20\times 0.5=10$

Millimoles (or milliequivalents) of$HCl=100\times 0.1=10$

$\therefore$ $\underset{10milliequivalents}{NaOH}+\underset{10milliequivalents}{HCl}⟶NaCl+H_{2}O$

Thus, heat released when $10$ milliequivalents of $HCl$ are neutralised by $10$ millimoles of $NaOH=xkJ$. But heat of neutralisation is heat released when $1$ equivalent of $HCl$ is neutralised by $1$ equivalent of $NaOH$.

$\therefore$ ${\Delta }_{neu}H=\frac{x}{10\times {10}^{-3}}$ or $-100xkJ/mol$