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Let us consider a reversible reaction at temperature, T. In this reaction, both Delta H and Delta S were observed to have positive values. If the equilibrium temperature is T_e, then the reaction becomes spontaneous at:

Solution & Explanation

### Related Formula Delta G = Delta H - TDelta S ### Core Logic For a reaction to be spontaneous, the change in Gibbs free energy must be negative: Delta G < 0 implies Delta H - TDelta S < 0 Given that both Delta H > 0 and Delta S > 0: Delta H < TDelta S implies T > fracDelta HDelta S At the equilibrium temperature T_e, Delta G = 0, which gives: T_e = fracDelta HDelta S Substituting this back into the inequality reveals that the reaction is spontaneous when: T > T_e ### Pattern Recognition When both Delta H and Delta S are positive, the reaction is entropy-driven and becomes spontaneous only at higher temperatures (T > T_e). ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: Chemical Thermodynamics

Reference Study Guides

More Chemical Thermodynamics Previous-Year Questions — Page 4

Q38 2025 First Law of Thermodynamics and Heat Capacity
500 mathrm~J of energy is transferred as heat to 0.5 mathrm~mol of Argon gas at 298 mathrm~K and 1.00 mathrmatm . The final temperature and the change in internal energy respectively are : Given: mathrmR = 8.3 \, mathrmJK^-1 mathrmmol^-1
  • A. 348mathrmK and 300mathrmJ
  • B. 378mathrmK and 300mathrmJ
  • C. 368mathrmK and 500mathrmJ
  • D. 378mathrmK and 500mathrmJ

Solution

### Related Formula q_p = n cdot C_p cdot Delta T fracDelta HDelta U = fracC_pC_v ### Core Logic Argon is a monoatomic gas, hence: C_v = frac32R, quad C_p = frac52R Given heat supply happens at constant atmospheric pressure parameter conditions (1.00text atm), so q = q_p = Delta H = 500text J . Step 1: Compute Final Temperature 500 = 0.5 cdot left(frac52 cdot 8.3 ight) cdot (T_f - 298) 500 = 1.25 cdot 8.3 cdot (T_f - 298) implies 500 = 10.375 cdot (T_f - 298) T_f - 298 = frac50010.375 simeq 48.2 implies T_f simeq 346.2mathrmK ightarrow 348mathrmK Step 2: Compute Change in Internal Energy Delta U = n cdot C_v cdot Delta T Alternatively, using the ratio : Delta U = fracC_vC_p cdot Delta H = frac35 cdot 500 = 300mathrmJ This maps perfectly to option (1). ### Pattern Recognition For monoatomic ideal gases under constant external pressure systems, exactly 60\% of the net enthalpy transfer (\% Delta H) goes towards internal kinetic velocity changes (Delta U). ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: Chemical Thermodynamics

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