For a reaction to be nonspontaneous under standard conditions at all temperatures, the signs of δh∘ and δs∘ must be and respectively.

For a reaction to be nonspontaneous under standard conditions at all temperatures, the signs of ΔH and ΔS must be positive and negative, respectively.
Gibbs free energy (G) determines if reaction will proceed spontaneously.
ΔG = ΔH - T·ΔS.
ΔG - changes in Gibbs free energy.
ΔH - changes in enthalpy.
ΔS - changes in entropy.
T is temperature in Kelvins.
When ΔS < 0 (negative entropy change) and ΔH > 0 (endothermic reaction), the process is never spontaneous (ΔG> 0).