Question

Identify each of the following changes of state as melting, freezing, sublimation, or deposition: a. The solid structure of a substance breaks down as liquid forms. b. Coffee is freeze-dried. c. Water on the street turns to ice during a cold wintry night. d. Ice crystals form on a package of frozen corn.

Short answer

a. Melting, b. Sublimation, c. Freezing, d. Deposition

Step-by-step solution

Identify the change for Part a

The solid structure of a substance breaks down as liquid forms. This process is called melting, where a solid turns into a liquid.

Identify the change for Part b

Coffee is freeze-dried. Freeze-drying involves removing water from the coffee in its frozen state, which means it goes directly from a solid (ice) to a gas (water vapor). This process is called sublimation.

Identify the change for Part c

Water on the street turns to ice during a cold wintry night. This process is called freezing, where a liquid turns into a solid.

Identify the change for Part d

Ice crystals form on a package of frozen corn. This process is called deposition, where a gas turns directly into a solid without going through the liquid phase.

Key concepts

melting

Melting is the process where a solid turns into a liquid. It happens when the solid absorbs heat.
When particles within the solid gain enough energy, they start to vibrate more vigorously.
Once they have enough energy, they break free from their fixed positions and begin to move freely, forming a liquid.
A common example of melting is ice turning into water.
This process happens at a specific temperature called the melting point.
For water, the melting point is 0°C (32°F).

• This process can be observed in everyday life, like when you leave ice cubes out at room temperature.
• Metals also melt when heated to high temperatures, making them moldable.

freezing

Freezing is the transformation of a liquid into a solid.
This happens when the liquid loses heat.
As the liquid cools down, the energy of its particles decreases.
These particles then move less and arrange themselves into fixed positions, forming a solid.
A typical example of freezing is water turning into ice.
This occurs at the same temperature as melting, known as the freezing point.

• For water, it is 0°C (32°F).
• Freezing is commonly seen when water turns into ice in your freezer.
• Biological samples are often frozen to preserve them for future use.

sublimation

Sublimation is a fascinating process where a solid changes directly into a gas without passing through the liquid state.
This typically happens under specific conditions of low pressure and high energy.
Sublimation requires a lot of energy to overcome both the attraction among solid particles and the forces keeping them in place.
A classic example of sublimation is dry ice (solid carbon dioxide) changing directly to carbon dioxide gas.
Sublimation is used in practical applications like freeze-drying food, which helps preserve it by removing moisture without compromising quality.

• Sublimation can also be observed when frost forms on windows and then disappears without turning into water.

deposition

Deposition is the process through which a gas changes directly into a solid, bypassing the liquid state.
This process is the opposite of sublimation and occurs under conditions where gas molecules lose enough thermal energy.
They slow down and arrange themselves into a solid structure.
A visible example of deposition is the formation of frost on cold surfaces.
This is when water vapor in the air settles onto a cold surface and changes directly into ice without becoming liquid first.
Deposition also occurs when soot forms directly from smoke in flames or fireplaces.

• Deposition can be used to coat surfaces with thin layers of solid material in various industrial applications.