નીચેની પ્રક્રિયાઓ વિચારો.

$(i)$ $H_{(aq)}^+ + OH^-= H_2O_{(l)} ,$ $\Delta H = -X_1\,kJ \,mol^{-1}$

$(ii)$ $H_{2(g)} + \frac{1}{2}O_{2(g)} = H_2O_{(l)},$ $\Delta H = -X_2\,kJ \,mol^{-1}$

$(iii)$ $CO_{2(g)} + H_{2(g)} = CO_{(g)} + H_2O_{(l)},$ $\Delta H = -X_3\, kJ\, mol^{-1}$

$(iv)$ $ C_2H_{2(g)}+ \frac{5}{2} O_{2(g)} = 2CO_{2(g)} + H_2O_{(l)},$ $\Delta H = -X_4\,kJ \,mol^{-1}$

તો $H_2O_{(l)}$ સર્જનઉષ્મા કેટલી હશે ?

Question

નીચેની પ્રક્રિયાઓ વિચારો.

$(i)$ $H_{(aq)}^+ + OH^-= H_2O_{(l)} ,$ $\Delta H = -X_1\,kJ \,mol^{-1}$

$(ii)$ $H_{2(g)} + \frac{1}{2}O_{2(g)} = H_2O_{(l)},$ $\Delta H = -X_2\,kJ \,mol^{-1}$

$(iii)$ $CO_{2(g)} + H_{2(g)} = CO_{(g)} + H_2O_{(l)},$ $\Delta H = -X_3\, kJ\, mol^{-1}$

$(iv)$ $ C_2H_{2(g)}+ \frac{5}{2} O_{2(g)} = 2CO_{2(g)} + H_2O_{(l)},$ $\Delta H = -X_4\,kJ \,mol^{-1}$

તો $H_2O_{(l)}$ સર્જનઉષ્મા કેટલી હશે ?

A$ +X_3\,kJ \,mol^{-1}$
B$ -X_4\,kJ \,mol^{-1}$
C$ +X_1\,kJ \,mol^{-1}$
D$ -X_2\,kJ \,mol^{-1}$

AIPMT 2007, Medium

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Solution

d
The standard enthalpy change of formation of a compound is the enthalpy change which occurs when one mole of the compound is formed from its elements under standard conditions. The equation showing the standard enthalpy change of formation of water is $H _{2}( g )+\frac{1}{2} O _{2}( g ) \longrightarrow H _{2} O (1)$

1 mole of water formed.

$\therefore$ Enthalpy of formation is $- X _{2} kJ / mol$.

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