# Question #a146a

##### 1 Answer

Here's why that it is so.

#### Explanation:

The spontaneity of a chemical reaction depends on **three factors**

These three factors are linked through something called the Gibbs free energy, which is the **only** criterion that determines whether or not a chemical process if spontaneous or not.

More specifically, you will have

#color(blue)(DeltaG = DeltaH - T * DeltaS)" "# , where

*change in Gibbs free energy* for the process

Now, in order for a process to be **spontaneous**, you need to have **nonspontaneous** process is described by

So, looking at the equation for the change in Gibbs free energy, you can say that **four distinct scenarios** can take place

#DeltaH<0# ,#DeltaS>0 -># *spontaneous at any temperature*#DeltaH>0# ,#DeltaS<0 -># *non-spontaneous regardless of temperature*#DeltaH>0# ,#DeltaS>0 -># *spontaneous at a certain temperature range*#DeltaH<0# ,#DeltaS<0 -># *spontaneous at a certain temperature range*

So, when solid water, or ice, **melts**, the process is endothermic, since you need to provide it with heat in order to disrupt the hydrogen bonds that are keeping the water molecules locked in place.

This means that you're in a case where **spontaneous** if you have

#DeltaS > 0 -># the entropy of the system isincreasing#T# ishigh enough

So, is the entropy of the system **increasing** when solid turns to liquid?

Indeed it is!

Remember, entropy is simply a measure of randomness and disorder. When compared with molecules in the solid state, which are *vibrating* in **fixed positions**, molecules in the liquid state re free to move around and bump into each other.

So, the only remaining factor that is important here is the **temperature** at which the reaction takes place,

As it turns out, this value of *solid* and the *liquid* states **are in equilibrium**.

You can thus say that

*when*#T < 0^@"C"# ,*the***melting**of ice is**nonspontaneous**, since

#DeltaG = DeltaH - T * DeltaS > 0#

*when*#T > 0^@"C"# ,*the***melting**of ice is**spontaneous**, since

#DeltaG = DeltaH - T * DeltaS < 0#

So, at temperatures above *entropy-driven* **spontaneous process**!