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5. Thermodynamics and thermochemistry — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistry5. Thermodynamics and thermochemistry1 Mark
MCQ
An organic compound $C_xX_YO_z$ on complete combustion provides equivolume of products $CO_2(g)$ and $H_2O(g)$ which is individually double the volume of organic compound taken. In the process volume of oxygen consumed is same as volume of $CO_2$ produced and liberated heat during combustion is $500 \ kcal/mole$ at constant pressure and at $500\ K$. Formula of organic compoun  & $\Delta U$ for reaction will be -
  • A
    $C_3H_6O_4, 501\ kcal/mole$
  • ✓
    $C_2H_4O_2, 499\ kcal/mole$
  • C
    $C_4H_8O_2, 1500\ kcal/mole$
  • D
    $C_2H_6O, 1500\ kcal/mole$
✓

Answer

Correct option: B.
$C_2H_4O_2, 499\ kcal/mole$
b
$\mathop {{{\text{C}}_{\text{x}}}{{\text{H}}_{\text{y}}}{{\text{O}}_{\text{z}}}}\limits_{\text{V}}  + \mathop {\left( {{\text{x}} + \frac{{\text{y}}}{4} - \frac{{\text{z}}}{2}} \right){{\text{O}}_2}}\limits_{{\text{V}}\left( {{\text{x}} + \frac{{\text{y}}}{4} - \frac{{\text{z}}}{2}} \right)}  \to \mathop {{\text{xC}}{{\text{O}}_2}}\limits_{{\text{Vx}}}  + \mathop {\frac{{\text{y}}}{2}{{\text{H}}_2}{\text{O}}}\limits_{\frac{{{\text{Vy}}}}{2}} $

$2 \mathrm{V}=\mathrm{V} \mathrm{x} \Rightarrow \mathrm{x}=2$

$2 \mathrm{V}=\frac{\mathrm{Vy}}{2} \Rightarrow \mathrm{y}=4$

$2 \mathrm{V}=\mathrm{V}\left(\mathrm{x}+\frac{\mathrm{y}}{4}-\frac{\mathrm{z}}{2}\right) \Rightarrow \mathrm{z}=2$

Formula $\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}_{2}$

$\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}_{2}+2 \mathrm{O}_{2} \rightarrow 2 \mathrm{CO}_{2}+2 \mathrm{H}_{2} \mathrm{O}$

$500=\Delta \mathrm{U}+(1) \times \frac{2}{1000} \times 500$

$\Delta \mathrm{U}=499\, \mathrm{kcal} / \mathrm{mole}$

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