Question

Consider two processes: sublimation of I2(s) and melting of I2(s) (Note: the latter process can occur at the same temperature but somewhat higher pressure).
I2(s) → I2(g)
I2(s) → I2(l)
Is ΔS positive or negative in these processes?

Answer 1

Answer:

positive

positive

Explanation:

Entropy -

In a system, the randomness is measured by the term entropy .

Randomness basically refers as a form of energy that can not be used for any work.

The change in entropy is given by amount heat per change in temperature.

• When solid is converted to gas entropy increases,

As the molecules in solid state are tightly packed and has more force of attraction between the molecules, but as it is converted to gas, the force of attraction between the molecule decreases and hence entropy increases.

So,

The particles of the substance , if are tightly held by strong force of attraction will decrease the entropy ,

And

If the particles are loosely held , the entropy will increase , i.e. , positive entropy .

Similar with solid converting to liquid , the entropy will increases , i.e. , positive entropy .

Hence ,

The correct sign of entropy for both the process is positive .

Answer 2

Answer:

ΔS increases in each case.  

Explanation:

Entropy (S) is a measure of the degree of the spreading of energy within a system. The more ways that energy can be distributed, the greater the entropy.

(a) Sublimation of I₂

I₂(s)⇌ I₂(g)

In the solid, the I₂ molecules are locked in position in a crystal lattice. They can vibrate only slightly about their equilibrium locations.  

Those in the gas phase can move in different directions and at different speeds, so the thermal energy is widely distributed among many microstates. The mobility of the molecules is greatly increased, so the number of number of microstates increases and entropy increases.

(b) Melting of I₂

I₂(s)⇌ I₂(ℓ)

The molecules in the solid can only vibrate about a fixed position.

Those in the liquid phase can move around and slide past each other. The increased freedom of motion means that thermal energy is distributed among more microstates, so the entropy increases.