Question

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

Answer 1

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`

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.