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Current Question (ID: 8351)

Question:
$\text{For the reaction A + B}$ $\rightarrow$ $\text{C + D + q (kJ/mol), entropy change is positive. The reaction will be}$ $\text{1. Possible only at high temperature}$ $\text{2. Possible only at low temperature}$ $\text{3. Not possible at any temperature}$ $\text{4. Possible at any temperature}$
Options:
  • 1. $\text{Possible only at high temperature}$
  • 2. $\text{Possible only at low temperature}$
  • 3. $\text{Not possible at any temperature}$
  • 4. $\text{Possible at any temperature}$
Solution:
$\text{Hint:}$ $\Delta\text{G} = \Delta\text{H} - \text{T}\Delta\text{S}$ $\text{To determine the temperature range at which the reaction is spontaneous, we need to analyze the Gibbs free energy equation:}$ $\Delta\text{G} = \Delta\text{H} - \text{T}\Delta\text{S}$ $\text{For a reaction to be spontaneous, }\Delta\text{G must be negative.}$ $\text{Given information:}$ $\text{- The reaction releases energy (q kJ/mol)}$ $\text{- The entropy change (}\Delta\text{S) is positive}$ $\text{Step 1: Identify the enthalpy change of the reaction.}$ $\text{Since the reaction releases energy (q kJ/mol), this indicates an exothermic reaction. For exothermic reactions, the enthalpy change is negative:}$ $\Delta\text{H} = -\text{q kJ/mol} < 0$ $\text{Step 2: Analyze the Gibbs free energy equation with the given parameters.}$ $\Delta\text{G} = \Delta\text{H} - \text{T}\Delta\text{S}$ $\text{With }\Delta\text{H} < 0\text{ and }\Delta\text{S} > 0\text{:}$ $\text{Both terms in the equation (}\Delta\text{H and -T}\Delta\text{S) are negative, which means }\Delta\text{G will always be negative, regardless of the temperature value.}$ $\text{This can be explained as follows:}$ $\text{- The negative }\Delta\text{H contributes to making }\Delta\text{G negative}$ $\text{- Since }\Delta\text{S is positive, the term -T}\Delta\text{S is negative (as T is always positive in Kelvin)}$ $\text{- The sum of two negative terms is always negative}$ $\text{Step 3: Determine the temperature range for spontaneity.}$ $\text{Since }\Delta\text{G is negative at all temperatures, the reaction will be spontaneous at any temperature.}$ $\text{When both enthalpy and entropy changes favor the reaction (}\Delta\text{H} < 0\text{ and }\Delta\text{S} > 0\text{), we have what is sometimes called an "entropy-enthalpy driven reaction" or "win-win situation" in thermodynamic terms. Such reactions are spontaneous under all conditions.}$ $\text{Therefore, the reaction is possible at any temperature, making option 4 the correct answer.}$

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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
}