Question

When $0.2$ mole of anhydrous $CuSO _4$ is dissolved in water, the heat evolved is $1.451\, kcal$.If $0.2$ mole of $CuSO _4 \cdot 5 H _2 O$ is dissolved in water, the heat absorbed is $0.264\, kcal$. Calculate the molar heat of hydration of $CuSO _4$.

Answer 1

$\text { (i) } CuSO _4( s )+ H _2 O \longrightarrow CuSO _4 \text { (aq) }$
$\Delta H =\frac{-1.451}{0.2}=-7.255 \,k\, cal\, mol ^{-1}$
(ii) $CuSO _4 \cdot 5 H _2 O (s) \longrightarrow CuSO _4 (aq) +5 H _2 O$
$\Delta H =\frac{0.264}{0.2}=1.32\, k \,cal\, mol ^{-1}$
From (i)-(ii),
$CuSO _4( s )+5 H _2 O ( l ) \longrightarrow CuSO _4 \cdot 5 H _2 O ( s )$;
$\Delta H =-8.575\, k \,cal \,mol ^{-1}$