Question

For a reaction for which AH = +29.3 kJ/mol and AS = +106 J/mol•K, which of the following statements is true? A) The reaction is spontaneous above 276 K. B) The reaction is spontaneous below 276 K. C) The reaction will never reach equilibrium. D) The reaction will never be spontaneous.

Answer 1

Answer: A) The reaction is spontaneous above 276 K.

Explanation:

According to Gibb's equation:

$\Delta G=\Delta H-T\Delta S$

$\Delta G$ = Gibbs free energy  

$\Delta H$ = enthalpy change  = +29.3 kJ/mol =29300 J/mol

$\Delta S$ = entropy change  = +106 J/molK

T = temperature in Kelvin

$\Delta G$= +ve, reaction is non spontaneous

$\Delta G$= -ve, reaction is spontaneous

$\Delta G$= 0, reaction is in equilibrium

$\Delta G=(+ve)-T(+ve)$

$\Delta G=(+ve)(-ve)$

$T\Delta S>\Delta H$  for reaction to be spontaneous

$T\times 106 J/molK>29300J/mol$

$T>276K$

Thus the Reaction is spontaneous when temperature is above 276 K.