Answer to Question #82216 in General Chemistry for Yusr

Question

The great majority of chemical reactions in nature are exothermic. As these reactions proceed, energy is liberated and the products have less energy than the original reactants. The products are also more resistant to change, more stable, than the original reactants. The tendency throughout nature is for a reaction to proceed in a direction that leads to a lower energy state. We might think that endothermic reactions, in which energy is absorbed, cannot occur spontaneously because the products are at higher potential energy and are less stable than the original reactants. They would be expected to proceed only with the assistance of an out- side influence, such as continued heating. However, some endothermic reactions do occur spontaneously. We conclude that something other than enthalpy change must help determine whether a reaction will occur?

Answer 1

When ΔH is negative and ΔS is positive, ΔG will be negative over all temperatures.

When ΔH is negative and ΔS is negative, ΔG will be negative at low temperatures.

When ΔH is positive and ΔS is negative, ΔG will not be negative at any temperature. There would be no spontaneous reaction.

When ΔH is positive and ΔS is positive, ΔG will be negative at high temperatures.

Therefore, finally it is the change in free energy of a reaction which can predict if a reaction is feasible.