Question

$100{cm}^3$ of $0.5N$ $HCl$ solution at $299.95K$ were mixed with $100{cm}^3$ $0.5N$ $NaOH$ solution at $299.75K$ in a thermos flask. The final temperature was found to be $302.65K$. Calculate the enthalpy of neutralisation of $HCl$. Water equivalent of thermos flask is $44g$.

Answer 1

The initial average temperature of the acid and the base
$=\frac{299.95+299.75}{2}=299.85K$
Rise in temperature $=(302.65-299.85)=2.80K$
Heat evolved during neutralisation
$=(100+100+44)\times 4184\times 2.8=2858J$
$\therefore$ Enthalpy of neutralisation $=-\frac{2858}{100}\times 1000\times \frac{1}{0.50}$
$=-57.17kJ$