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Thermodynamics — Chemistry STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 ScienceChemistryThermodynamics3 Marks
Question
Justify the following statements.
  1. Reactions with $\Delta\text{G}<0$ always have an equilibrium constant greater than 1.
  2. Many thermodynamically feasible reactions do not occur under ordinary conditions.
  3. At low temperatures, enthalpy change dominates the $\Delta\text{G}$ expression and at high temperatures, it is the entropy which dominates the value of $\Delta\text{G}.$
✓

Answer

  1. $\Delta\text{G}=-2.303\text{RT}\log\text{K}.$ Thus, when $\Delta\text{G}^\circ<0,$ K > 1).
  2. Under ordinary conditions, the average energy of the reactants may be less than threshold energy. They require some activation energy to initiate the reaction.
  3. $\Delta\text{G}=​​\Delta\text{H}-\text{T}\Delta\text{S}.$ At low temperature, $\text{T}\Delta\text{S}$ is small. Hence, $\Delta\text{H}$ dominates. At high temperature, $\text{T}\Delta\text{S}$ is large, i.e. $\Delta\text{S}$ dominates the value of $\Delta\text{G}.$

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