What happens when delta S is negative and delta H is positive?

When the change in entropy (delta S) is negative, it indicates that the disorder of the system is decreasing. Conversely, a positive change in enthalpy (delta H) suggests that the system is absorbing heat from its surroundings, which typically favors an increase in disorder. These conditions—negative delta S and positive delta H—reflect a situation where a process tends to move towards greater order while requiring heat input, which is not favorable for spontaneity.

In thermodynamics, a process is considered spontaneous if it can occur without the input of external energy. When both delta S is negative and delta H is positive, the combination suggests that the overall free energy change (delta G, calculated as delta G = delta H - T * delta S) will be positive at all temperatures. A positive delta G means that the process cannot occur spontaneously; however, the reverse process, which would result in increased disorder, would be spontaneous since it would yield a negative delta G.

So, in this scenario, not only is the direct process non-spontaneous under all conditions, but it also suggests the existence of a reverse spontaneous process, where entropy would increase, leading to a negative change in free energy.