Question

$H_2(g) + \frac{1}{2}O_2(g) \to H_2O(l)$
$H_2O_{(l)} \to H_2O_{(g)} ; \Delta H = x_4$
Given, $E_{H - H} = x_1$
$E_{O = O} = x_2$
$E_{O - H} = x_3$
$\Delta H_F$ of $H_2O$ vapour is

• A. $x_{1}+\frac{x_{2}}{2}-x_{3}+x_{4}$
• B. $2 x _{3}- x _{1}-\frac{ x _{2}}{2}- x _{4}$
• C. $x_{1}+\frac{x_{2}}{2}-2 x_{3}-x_{4}$
• D. $x_{1}+\frac{x_{2}}{2}-2 x_{3}+x_{4}$

Answer 1

Answer: (D)

Now, for $H _{2}( g )+\frac{1}{2} O _{2}( g ) \longrightarrow H _{2} O (\ell) ; \Delta H$
$\Delta H =( B . D . E )_{\text {reactants }}-( B . D . E )_{\text {products }}$
$= x _{1}+\frac{1}{2} x _{2}-2 x _{3}$
$\Delta H _{ f }=\Delta H + x _{4}$
$= x _{1}+\frac{1}{2} x _{2}-2 x _{3}+ x _{4}$