Question

If the ΔH = 175 kJ/mol and ΔS = 96 J/K mol for a non spontaneous reaction, at what temperature does this reaction become spontaneous?

Answer 1

Spontaneity of Reactions

Gibbs Free Energy (
`\Delta G`) tells us whether or nor a reaction is spontaneous. If it is negative, it is, and if it is positive, it is not spontaneous.

`\Delta G` = 0 when a reaction first becomes spontaneous, because it is the first non-positive number.

Solving the Question

It is important to note this equation:

`\Delta G = \Delta H-T\Delta S`

Rearrange the equation to solve for T:

`T=-(\Delta G-\Delta H)/(\Delta S)`

Plug in the given information:

`T=-(0-175)/(0.096)` (notice how we converted J to kJ)

`T=(175)/(0.096)`

`T=1822.9`

Round to two significant figures:

1800

Answer

At 1800 K, the reaction will become spontaneous.