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Current Question (ID: 8346)
Question:
$\text{The entropy change in the conversion of one mole of liquid water at 373 K to vapour at the same temperature would be: (Latent heat of vaporization of water,}$ $\Delta H_{vap} = 2.257 \text{ kJ/g)}$
Options:
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1. $105.9 \text{ JK}^{-1}\text{mol}^{-1}$
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2. $107.9 \text{ JK}^{-1}\text{mol}^{-1}$
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3. $108.9 \text{ JK}^{-1}\text{mol}^{-1}$
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4. $109.9 \text{ JK}^{-1}\text{mol}^{-1}$
Solution:
$\text{Hint:}$ $\Delta\text{S}_{vap} = \frac{\Delta\text{H}_{vap}}{\text{T}}$
$\text{To calculate the entropy change during the vaporization of water at its boiling point, we can use the formula:}$
$\Delta\text{S}_{vap} = \frac{\Delta\text{H}_{vap}}{\text{T}}$
$\text{Where:}$
$\Delta\text{S}_{vap} = \text{entropy change of vaporization}$
$\Delta\text{H}_{vap} = \text{enthalpy change of vaporization (latent heat)}$
$\text{T} = \text{temperature in Kelvin}$
$\text{Given information:}$
$\Delta\text{H}_{vap} = 2.257 \text{ kJ/g}$
$\text{T} = 373 \text{ K}$
$\text{Step 1: Calculate the entropy change per gram of water.}$
$\Delta\text{S}_{vap} = \frac{\Delta\text{H}_{vap}}{\text{T}}$
$\Delta\text{S}_{vap} = \frac{2.257 \text{ kJ/g}}{373 \text{ K}}$
$\text{Converting kJ to J:}$
$\Delta\text{S}_{vap} = \frac{2.257 \times 10^3 \text{ J/g}}{373 \text{ K}}$
$\Delta\text{S}_{vap} = 6.05 \text{ JK}^{-1}\text{g}^{-1}$
$\text{Step 2: Calculate the entropy change for one mole of water.}$
$\text{The molar mass of water (H}_2\text{O) is 18 g/mol.}$
$\text{So, for one mole of water:}$
$\Delta\text{S}_{vap} (\text{per mole}) = 6.05 \text{ JK}^{-1}\text{g}^{-1} \times 18 \text{ g/mol}$
$\Delta\text{S}_{vap} (\text{per mole}) = 108.9 \text{ JK}^{-1}\text{mol}^{-1}$
$\text{Therefore, the entropy change in the conversion of one mole of liquid water at 373 K to vapor is 108.9 JK}^{-1}\text{mol}^{-1}\text{, which corresponds to option 3.}$
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