Question

Which of the following processes will have a positive value of ΔS for the system? In other words, for which processes will the entropy will increase? If you aren't sure, find the equation you need and plug in some sample numbers.

		Mixing of two gases
		Compression of a gas
		Expansion of a gas
		Freezing
		Heating
		Boiling
		Condensing
		Cooling
		Melting

Answer 1

1entropy change of mixing = -RT*(x1*lnx1+x2*lnx2+ + +    )

since x1= mole fraction of component <1, lnx1 will be -ve, giving rise to entropy of mixing +ve.

2. Entropy is degree of disorder. During compression, the degree of diorder decreases. So entropy decreases

3. During expansion, the degree of disorder increases. hence entropy increases.

4. . During Freezing, the degree of disorder decreases as liquid state becomes solid where the molecules are more organized. Hence, during Freezing entropy decreases.

5.During heating, the molecular motion becomes more disordered, entropy increases.

6. Boiling increases the molecular movement making the liquid more disordered. Hence entropy increases.

7. condensing decreases the degree of disorder and entropy of gas is more than that of liqud which in turn is more than that of a solid. Hence during condesnation, gas starts to become liquid and this reduces the entropy.

8. during cooling, the degree of disorder decreases and hence entropy also decreases.

9. when melting takes place, a solid is converted to liquid which adds to degree of disorder. Hence entropy increases.