Question

Comment on the validity of the following statements, giving reasons : (i) Thermodynamically, an exothermic reaction is sometimes not spontaneous. (ii) The entropy of steam is more than that of water at its boiling point. (iii) The equilibrium constant for a reaction is one or more if $\triangle_rG\textdegree$ for it is less than zero.

Answer 1

• ΔG = ΔH−TΔS, this is the equation for Gibbs free energy where T is absolute temperature and ΔS is change in entropy. Hence, this expression of free energy that determines whether reaction is spontaneous and not the enthalpy. If Gibb’s free energy is negative the process shall be spontaneous.  

• The condensation of steam is a very exothermic reaction but we also know that the change in entropy is negative because as compared to gas liquids are more orderly and hence the reaction is spontaneous only at low temperature.

• According to Le chatlier’s principle, if there is a stress in any equilibrium reaction like a change in temperature the reaction tries to shift to reach an equilibrium again. Thus, when change in temperature is less than zero the equilibrium constant shall be one or more.

Answer 2

Explanation:

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