Final answer:
When ΔH is positive and ΔS is negative, the reaction is enthalpically favorable and entropically unfavorable.
Step-by-step explanation:
When ΔH is positive and ΔS is negative, the reaction is enthalpically favorable and entropically unfavorable. This means that the reaction is driven by the enthalpy change (heat released or absorbed), but the entropy change (degree of disorder) works against the reaction. In other words, even though the reaction releases energy, it results in a decrease in disorder. Therefore, both enthalpy and entropy are working in opposite directions, making the overall reaction unfavorable.