How does temperature affect the spontaneity of a reaction?

1 Answer
Mar 13, 2017

Answer:

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"#