Problem 25 - Chemistry An Atoms First Approach

Question

Which of the following processes are spontaneous? a. Salt dissolves in \(\mathrm{H}_{2} \mathrm{O}\). b. A clear solution becomes a uniform color after a few drops of dye are added. c. Iron rusts. d. You clean your bedroom.

Step-by-Step Solution

Answer

Processes a, b, and c (salt dissolving in \(\mathrm{H}_{2} \mathrm{O}\), a clear solution becoming uniform in color, and iron rusting) are spontaneous as they result in an increase in entropy and involve energy changes favorable for the process to occur. Process d (cleaning your bedroom) is non-spontaneous as it requires manual effort and results in a decrease in entropy.

Step 1: Process a: Salt dissolves in \(\mathrm{H}_{2} \mathrm{O}\).

Dissolving salt in water is a spontaneous process because it causes an increase in entropy (disorder) by mixing the salt and water molecules. Moreover, during this process, the energy is released (exothermic), making it favorable.

Step 2: Process b: A clear solution becomes a uniform color after a few drops of dye are added.

This process is also spontaneous, as the dye molecules spread throughout the solution, increasing its entropy. Diffusion is a natural process, and the dye particles move randomly from a high concentration to a low concentration region, resulting in a uniform color without any external assistance.

Step 3: Process c: Iron rusts.

Rusting of iron is a spontaneous process as it is an oxidation reaction. When iron is exposed to oxygen and moisture, it reacts to form rust (iron oxide), which is a more stable compound. This reaction releases energy, and the entropy increases due to the formation of more moles from the reactants, which makes this process spontaneous.

Step 4: Process d: You clean your bedroom.

Cleaning your bedroom is not a spontaneous process, as it requires your manual effort to organize the items and clean the space. It also involves a decrease in entropy (disorder) as the bedroom becomes more organized after cleaning. Therefore, this process is non-spontaneous. From the above analysis, processes a, b, and c are spontaneous, while process d is not spontaneous.