Question

The heat of formation of water from $H^{+}$ and ${OH}^{-}$ is :

• A. $13.06kcal$
• B. $-13.06kcal$
• C. $16.32kcal$
• D. $-16.32kcal$

Answer 1

The correct option is B $-13.06kcal$

At ${25}^{o}C$, $pH=7$
$\therefore K_w={10}^{-14}$; At ${60}^{o}C$, $pH=6.5$
$\therefore K_w={10}^{-13}$
$H_{2}O\rightleftharpoons H^{+}+{OH}^{-};\Delta H=?$
$2.303\log \frac{{10}^{-13}}{{10}^{-14}}=\frac{\Delta H}{R}\left[\frac{35}{333\times 298}\right]$
$\therefore \Delta H=13.06kcal$
$H^{+}+{OH}^{-}⟶H_{2}O;\Delta H=-13.06kcal$