Identify the following processes as spontaneous or not.

A. Identify the following processes as spontaneous or not.

1. Cooling of a hot flat iron
2. Drop of ink dispersing in water
3. Straightening curly hair
4. Cold water warming to room temperature
5. Sorting names alphabetically
6. Black hair turning grey
7. Wind scattering leaves in a pile
8. Shovelling snow
9. Removing stain from a stain
10. Sublimation of naphthalene in a room temperature

B. Predict whether the entropy increases or decreases for each of the following processes. Consider the degree of disorder, from initial to final state or from reactants to products.

11. Sublimation of dry ice: CO2(s) ? CO2(g)
12. Na-1(aq) + Cl-1(aq) ? NaCl
13. 2NH3(g) ? N2(g) + 3H2(g)
14. Lowering the temperature of ethyl alcohol from 30 degree Celsius to 10 degree Celsius
15. Dissolving food color in water

THE CORRECT ANSWER AND EXPLANATION IS:

Entropy Predictions and Explanations

Entropy is a thermodynamic property that refers to the level of disorder or randomness in a system. A system with more microstates, greater molecular movement, or higher energy distribution typically has higher entropy. When analyzing a process, one should compare the disorder before and after the change. Below are predictions for the given processes:

Sublimation of dry ice: CO₂(s) → CO₂(g)
Entropy increases

In sublimation, carbon dioxide transitions directly from solid to gas. Solids have highly ordered structures, while gases are highly disordered with particles moving freely in all directions. This transition results in a major increase in molecular randomness, indicating a significant increase in entropy.

Na⁺(aq) + Cl⁻(aq) → NaCl(s)
Entropy decreases

This process involves the combination of two dissociated aqueous ions to form a solid salt. In the aqueous state, ions move independently in solution, creating a highly disordered system. When these ions form a crystalline solid, they become fixed in a lattice structure, significantly decreasing the system’s disorder. Therefore, entropy decreases.

2NH₃(g) → N₂(g) + 3H₂(g)
Entropy increases

This chemical reaction starts with two moles of ammonia gas and ends with four moles of gas (one mole of nitrogen and three moles of hydrogen). More gas molecules means more possible positions and energy distributions. Additionally, smaller molecules like hydrogen move faster and are more disordered. Hence, this reaction leads to an increase in entropy.

Lowering the temperature of ethyl alcohol from 30°C to 10°C
Entropy decreases

Reducing temperature slows down the movement of molecules, which reduces randomness. The molecules in colder ethyl alcohol vibrate and move less than they do at a higher temperature. Therefore, the entropy decreases as the system becomes more ordered.

Dissolving food color in water
Entropy increases

This process involves a solid or concentrated drop dispersing into water. Initially, the dye particles are in a compact form. As they dissolve, they spread out randomly among water molecules. This mixing increases the number of microstates available and raises the system’s disorder, resulting in an increase in entropy.