# How does temperature affect the spontaneity of a reaction?

Mar 13, 2017

Spontaneity depends on the sign of ΔG.

#### Explanation:

There are three possible situations:

• If ΔG < 0, the reaction is spontaneous in the forward direction.
• If ΔG = 0, the reaction is at equilibrium.
• If ΔG > 0, the reaction is not spontaneous in the forward direction, but it is spontaneous in the reverse direction.

The value of ΔG depends on temperature:

color(blue)(bar(ul(|color(white)(a/a)ΔG = ΔH - TΔScolor(white)(a/a)|)))" "

Now, we have four possible situations, depending on the signs of ΔH and ΔS:

bb(ΔHcolor(white)(m)ΔS color(white)(mmm)"High Temp."color(white)(mmmmmm)"Low Temp.")
color(white)(l)+color(white)(ml)+ color(white)(m)ΔG -; "spontaneous"color(white)(mmm)ΔG +; "not spontaneous"
color(white)(l)+color(white)(ml)- color(white)(m)ΔG +; "not spontaneous"color(white)(m)ΔG +; "not spontaneous"
color(white)(l)-color(white)(ml)+ color(white)(m)ΔG -; "spontaneous"color(white)(mmm)ΔG -; "spontaneous"
color(white)(l)-color(white)(ml)- color(white)(m)ΔG +; "not spontaneous"color(white)(m)ΔG -; "spontaneous"