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Current Question (ID: 8340)

Question:
\text{For exothermic reaction to be spontaneous } (\Delta S \text{ = negative}) \text{ temperature must be:} \begin{array}{cccc} \text{1. High} & \text{2. Zero} & \text{3. Constant} & \text{4. Low} \end{array}
Options:
  • 1. $\text{High}$
  • 2. $\text{Zero}$
  • 3. $\text{Constant}$
  • 4. $\text{Low}$
Solution:
$\text{Hint: For a spontaneous reaction, }\Delta\text{G must be -ve.}$ $\text{To determine when an exothermic reaction with negative entropy change is spontaneous, we need to analyze the Gibbs free energy equation:}$ $\Delta\text{G} = \Delta\text{H} - \text{T}\Delta\text{S}$ $\text{For a reaction to be spontaneous, }\Delta\text{G must be negative.}$ $\text{Given information:}$ $\text{- The reaction is exothermic, so }\Delta\text{H is negative}$ $\text{- The entropy change (}\Delta\text{S) is negative}$ $\text{Substituting into the Gibbs equation:}$ $\Delta\text{G} = \Delta\text{H} - \text{T}\Delta\text{S}$ $\text{Since }\Delta\text{S is negative, the term -T}\Delta\text{S will be positive (a negative multiplied by a negative is positive).}$ $\text{For the reaction to be spontaneous, we need:}$ $\Delta\text{G} < 0$ $\text{Therefore:}$ $\Delta\text{H} - \text{T}\Delta\text{S} < 0$ $\Delta\text{H} < \text{T}\Delta\text{S}$ $\text{However, since both }\Delta\text{H and }\Delta\text{S are negative, we need to be careful with the inequality. When we divide both sides by the negative }\Delta\text{S, the inequality flips:}$ $\frac{\Delta\text{H}}{\Delta\text{S}} > \text{T}$ $\text{This means T must be less than }\frac{\Delta\text{H}}{\Delta\text{S}}\text{. In other words, temperature must be low for the reaction to be spontaneous.}$ $\text{At high temperatures, the T}\Delta\text{S term would become more significant, potentially making }\Delta\text{G positive and the reaction non-spontaneous.}$ $\text{Therefore, the answer is option 4: Low temperature.}$

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Expected JSON Format:

{
  "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
}