Final answer:
The processes with positive entropy changes are water evaporation and sodium chloride dissolving in water, as both lead to an increase in disorder within the system. Dry ice sublimation also results in a positive entropy change as it transitions from solid to gas. The formation of a lipid membrane would result in a negative entropy change due to increased order.
Step-by-step explanation:
The student is asking which of the listed processes have a positive entropy change. Entropy is a measure of the disorder or randomness in a system, and typically an increase in entropy (positive entropy change) occurs when the system becomes more disordered. Examples where entropy increases are when a substance changes from a solid to liquid or gas phase since the particles have more freedom of movement and hence, the number of possible ways the system can be arranged increases. Accordingly:
- Water evaporation has a positive entropy change since it involves a transition from liquid to gas, which increases disorder.
- Sodium chloride dissolving in water results in a positive entropy change, as the ions spread out and the structure becomes more disordered.
- Dry ice subliming also brings about a positive entropy change due to the phase transition from solid to gas, which significantly increases disorder.
- However, when different types of lipid molecules assemble to form a membrane, the process has a negative entropy change since it involves the system becoming more ordered.
Based on this understanding, we can determine that among the options provided, the processes in (a) water evaporation and sodium chloride dissolves in water, and (b) dry ice sublimes, would have positive entropy changes.