Question

How does temperature affect the spontaneity of a reaction?

Answer 1

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"`