When the sine of ΔG is unknown, we can say that the spontaneity of a reaction can predict it from the signs of enthalpy, which is ΔH, and entropy, which is ΔS. So here we're going to say that when they're both positive, we are spontaneous at high temperatures. And if both of them being positive makes it spontaneous at high temperatures, then what happens when it's the opposite? Well, when they're both negative, we'd be spontaneous at low temperatures.
Next we're going to say when ΔH is positive and ΔS is negative, you are always non spontaneous in terms of your chemical reaction. And if we do the opposite of that, if ΔH is now negative and ΔS is positive then you'd be spontaneous for your chemical reaction.
So just remember, easiest way to remember this here your ΔH positive and negative. Huge ΔS positive and negative. So you'd say high T, low T, non and spawn. So the sides of our ΔH and ΔS for chemical reaction can be used to determine the right temperature conditions to make it spontaneous or not.