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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:
  • 1. $105.9 \text{ JK}^{-1}\text{mol}^{-1}$
  • 2. $107.9 \text{ JK}^{-1}\text{mol}^{-1}$
  • 3. $108.9 \text{ JK}^{-1}\text{mol}^{-1}$
  • 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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{
  "question": "The mass of carbon present in 0.5 mole of $\\mathrm{K}_4[\\mathrm{Fe(CN)}_6]$ is:",
  "options": [
    {
      "id": 1,
      "text": "1.8 g"
    },
    {
      "id": 2,
      "text": "18 g"
    },
    {
      "id": 3,
      "text": "3.6 g"
    },
    {
      "id": 4,
      "text": "36 g"
    }
  ],
  "solution": "\\begin{align}\n&\\text{Hint: Mole concept}\\\\\n&1 \\text{ mole of } \\mathrm{K}_4[\\mathrm{Fe(CN)}_6] = 6 \\text{ moles of carbon atom}\\\\\n&0.5 \\text{ mole of } \\mathrm{K}_4[\\mathrm{Fe(CN)}_6] = 6 \\times 0.5 \\text{ mol} = 3 \\text{ mol}\\\\\n&1 \\text{ mol of carbon} = 12 \\text{ g}\\\\\n&3 \\text{ mol carbon} = 12 \\times 3 = 36 \\text{ g}\\\\\n&\\text{Hence, 36 g mass of carbon present in 0.5 mole of } \\mathrm{K}_4[\\mathrm{Fe(CN)}_6].\n\\end{align}",
  "correct_answer": 4
}