A chemical reaction cannot occur at all if its :

$∆\mathrm{G}=∆\mathrm{H}-\mathrm{T}∆\mathrm{S}$

When $∆\mathrm{H}=+\mathrm{ve};\mathrm{and} ∆\mathrm{S}=-\mathrm{ve}$,under these conditions $∆\mathrm{G}=+\mathrm{ve}$ and reaction is non -spontaneous in the given direction