Or a particular reaction, Δ H ∘ = − 16.1 kJ and Δ S ∘ = − 21.8 J/K. Assuming these values change very little with temperature, at what temperature does the reaction change from nonspontaneous to spontaneous?

Reaction is non-spontaneous when T > 738.5K and spontaneous when T < 738.5K

Explanation:

A reaction is non-spontaneous when ΔG° > 0 and is spontaneous when ΔG° < 0

ΔG° is defined as:

ΔG° = ΔH° - TΔS°

ΔG° will be > 0 (non-spontaneous) when  ΔH° > TΔS° and vice versa. Thus:

-16100J > T × -21.8J/K

738.5K > T

That means the reaction is non-spontaneous when T > 738.5K and spontaneous when T < 738.5K

I hope it helps!

a corroding iron, if that's one of your choices