What occurs when both ΔH and ΔS are positive?

When both the change in enthalpy (ΔH) and the change in entropy (ΔS) are positive, the spontaneity of the reaction can be understood through the Gibbs free energy equation:

[ \Delta G = \Delta H - T \Delta S ]

where ( \Delta G ) represents the change in Gibbs free energy, and ( T ) is the temperature in Kelvin. For a reaction to be spontaneous, the condition is that ( \Delta G ) must be negative.

Since ΔH is positive, it indicates that the reaction is endothermic, which means that heat is absorbed during the reaction. At low temperatures, this positive enthalpy contribution can lead to a situation where ( \Delta G ) is positive, making the reaction nonspontaneous.

However, because ΔS is also positive, it signifies an increase in disorder or randomness in the system. As the temperature increases, the term ( T \Delta S ) becomes more significant. Eventually, as the temperature rises sufficiently high, the positive contributions from the entropy will outweigh the positive enthalpy term. At this point, ( \Delta G ) can become negative, leading to spontaneous behavior.

Thus, the reaction becomes spontaneous as