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

Gujarat BoardEnglish MediumSTD 11 ScienceChemistry5. Thermodynamics and thermochemistry1 Mark
MCQ
$9.0 \,gm$ of $H_2O$ is vaporised at $100\,^oC$ and $1\,atm$ pressure. If the latent heat of vaporisation of water is $xJ / \, gm$, then $DS$ is given by :-
  • A
    $\frac{x}{373}$
  • B
    $\frac{18x}{100}$
  • C
    $\frac{18x}{373}$
  • ✓
    $\frac{1}{2} \times \frac{18x}{373}$
✓

Answer

Correct option: D.
$\frac{1}{2} \times \frac{18x}{373}$
d
$\Delta S=\frac{\Delta H_{v a p}}{T_{b}}$

where,

$\Delta S=$ change in entropy

$\Delta H_{v a p}=$ change in enthalpy of vaporization $=(x) \,J / g=(9 x)\, J$

$T_{b}=$ boiling point temperature $=100^{\circ} C =273+100=373\, K$

Now put all the given values in the above formula, we get:

$\Delta S=\frac{\Delta H_{vap}}{T_{b}}$

$\Delta S=\frac{(9\, x) g}{373 \,K}$

$\Delta S=(0.0241\, x)\, J / K$

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