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

Sep 14, 2017

Spontaneous only at high temperatures.

#### Explanation:

At constant Temperature, and constant pressure, the change Gibbs free energy is defined as:
$\Delta G = \Delta H - t \Delta S$

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

Finding the possible outcomes of different signs of $\Delta H , \Delta S$

When $\Delta H$ is positive $t \Delta S$ has to be bigger than $\Delta H$ so that the resulting sum would be negative, since when $t \Delta S$ is bigger than$\Delta H$, subtracting $t \Delta S$ from $\Delta H$ 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 $t \Delta S$ .

$\rightarrow \Delta H - t \Delta S$ is negative at higher temperature, and therefore the change in Gibbs energy is negative, and the reaction is spontaneous.