How will temperature affect the spontaneity of a reaction with positive #DeltaH# and #DeltaS#?

1 Answer
Sep 14, 2017

Answer:

Spontaneous only at high temperatures.

Explanation:

At constant Temperature, and constant pressure, the change Gibbs free energy is defined as:
#DeltaG=DeltaH-tDeltaS#

If the change in Gibbs free energy is negative, then the reaction will be spontaneous.

Finding the possible outcomes of different signs of #DeltaH, Delta S#
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When #DeltaH# is positive #tDeltaS# has to be bigger than #DeltaH# so that the resulting sum would be negative, since when #tDeltaS# is bigger than#DeltaH#, subtracting #tDeltaS# from #DeltaH# would be negative.

Since we suppose #Delta S#, is constant for a certain reaction, then we have to increase the temperature of to increase the value of #tDeltaS# .

#rarr DeltaH-tDeltaS# is negative at higher temperature, and therefore the change in Gibbs energy is negative, and the reaction is spontaneous.