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For a reaction with ΔH = 35.5 kJ mol⁻¹ and ΔS = 83.6 J K⁻¹ mol⁻¹, at what temperature condition will the reaction be spontaneous? (Assume ΔH and ΔS remain constant with temperature.)

1. T > 425 K
2. Spontaneous at every temperature
3. T < 298 K
4. T < 425 K

Correct answer: T > 425 K

Solution

The reaction will be spontaneous when the Gibbs free energy change (ΔG) is negative, which occurs when the temperature is high enough to overcome the positive enthalpy change (ΔH) by utilizing the positive entropy change (ΔS). By calculating the temperature at which ΔG equals zero, we find that it is above 425 K, making option A the correct choice.

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