Understanding Why Naphthalene Balls Disappear

Naphthalene balls are commonly used to repel moths and insects from clothes. You might have noticed that over time, these balls shrink and eventually disappear without ever seeming to melt into a liquid. This observation helps us understand the physical process responsible.

The Process Behind Naphthalene Disappearance

The disappearance of naphthalene balls is a classic example of a specific phase transition. Matter can exist in different states: solid, liquid, and gas. Usually, a solid first melts into a liquid and then evaporates into a gas when heated. However, some substances can bypass the liquid state entirely and transition directly from a solid to a gas. This process is called sublimation.

Naphthalene is one such substance. At room temperature and atmospheric pressure, naphthalene molecules have enough energy to overcome the intermolecular forces holding them in a solid structure and directly escape into the air as a gas.

Analyzing the Options

• Sublimation: This is the process where a solid changes directly into a gas without passing through the liquid state. Naphthalene exhibits this property at standard conditions, causing the solid ball to shrink and vanish over time as it converts into naphthalene vapor.
• Melting and Evaporation: Melting is the transition from solid to liquid, and evaporation is the transition from liquid to gas. Naphthalene balls do not typically melt at room temperature. Therefore, a process involving melting followed by evaporation is not the primary reason for their disappearance under normal conditions.
• Melting: This is just the solid-to-liquid transition. Naphthalene balls disappear as a gas, not by becoming a liquid puddle.
• Evaporation: This is the liquid-to-gas transition. Since naphthalene doesn't melt into a liquid at room temperature, evaporation is not the process by which the solid ball disappears.

Based on the properties of naphthalene and the definitions of the phase transitions, the disappearance of naphthalene balls is due to sublimation.

Key Points about Naphthalene and Sublimation

• Naphthalene is a solid compound.
• At typical room temperatures, it undergoes sublimation.
• Sublimation is the direct transition from solid to gas.
• This process causes the solid naphthalene ball to gradually turn into a gas and disappear.

Therefore, the correct process explaining why a naphthalene ball disappears is sublimation.

Revision Table: Naphthalene and Phase Changes

Additional Information: States of Matter and Transitions

Matter exists primarily in three states: solid, liquid, and gas. These states can change from one to another depending on temperature and pressure. These changes are called phase transitions.

• Solid: Particles are tightly packed in a fixed arrangement. Definite shape and volume.
• Liquid: Particles are close together but can move around. Definite volume but takes the shape of the container.
• Gas: Particles are far apart and move randomly. No definite shape or volume; fills the entire container.

Sublimation is a less common but important phase transition. Other substances that sublime include dry ice (solid carbon dioxide) and iodine. The reverse process of sublimation, where a gas changes directly into a solid, is called deposition or desublimation.

Understanding phase transitions helps explain many everyday phenomena, including why wet clothes dry (evaporation) or why ice melts (melting).