The entropy will usually increase when
I. a molecule is broken into two or more smaller molecules.
II. a reaction occurs that results in an increase in the number of moles of gas.
III. a solid changes to a liquid.
IV. a liquid changes to a gas.
(a) I only
(b) II only
(c) III only
(d) IV only
(e) I, II, III, and IV
The Correct Answer and Explanation is :
The correct answer is (e) I, II, III, and IV.
Here’s a breakdown of each statement:
I. A molecule is broken into two or more smaller molecules.
- This process typically leads to an increase in entropy because when a large molecule breaks down into smaller molecules, the system becomes more disordered. The number of possible arrangements of particles increases, which corresponds to a higher level of randomness or entropy.
II. A reaction occurs that results in an increase in the number of moles of gas.
- Gases have a higher entropy than liquids and solids because gas molecules are more spread out and have more freedom of movement. When the number of moles of gas increases, there are more molecules in the system that can move freely, which increases the disorder and entropy.
III. A solid changes to a liquid.
- The transition from solid to liquid (melting) generally leads to an increase in entropy. In a solid, the particles are closely packed and organized, whereas in a liquid, the particles are more disordered and move more freely. This increase in randomness is associated with an increase in entropy.
IV. A liquid changes to a gas.
- When a liquid evaporates to form a gas, there is a significant increase in entropy. Gas molecules are more spread out and have more freedom of motion compared to liquid molecules, which are more constrained. This increase in the number of available microstates results in higher entropy.
In summary, entropy tends to increase whenever the system becomes more disordered or when the number of possible arrangements of particles increases. All the processes listed—breaking a molecule into smaller ones, increasing the number of gas molecules, and the phase transitions from solid to liquid or liquid to gas—result in greater disorder, which corresponds to an increase in entropy. Hence, I, II, III, and IV all lead to an increase in entropy, making (e) the correct answer.