Question

During a very cold winter, the temperature may remain below freezing for extended periods. However, fallen snow can still disappear, even though it cannot melt. This is possible because a solid can vaporize directly, without passing through the liquid state. Is this process (sublimation) a physical or a chemical change?

Short answer

Sublimation is a process in which a solid substance transitions directly into a gas phase without going through a liquid phase. During the sublimation process, the substance does not undergo any changes in its chemical composition. The water molecules in the solid phase (ice) transition directly to the gas phase (water vapor), but the H2O molecules remain unchanged. Since sublimation does not cause any changes in the chemical composition of the substance (snow), it can be classified as a physical change. In this process, only the state of the substance changes from the solid phase to the gas phase, while the chemical composition remains the same.

Step-by-step solution

Define physical changes

A physical change is a change in the state or properties of a substance without altering its composition. Examples of physical changes include a change of state (solid, liquid, gas, or plasma), shape, size, or color. However, the substance's chemical composition remains the same. #Step 2: Define chemical changes#

Define chemical changes

A chemical change, also known as a chemical reaction, is a process in which one or more substances are transformed into new substances with different properties and composition. Examples of chemical changes include burning, rusting, and oxidation. During a chemical change, the chemical composition of the substance(s) is altered. #Step 3: Understand sublimation process#

Understand sublimation process

Sublimation is a process in which a solid substance transitions directly into a gas phase without going through a liquid phase. This occurs when the temperature and pressure conditions allow the molecules in the solid phase to gain enough energy to move directly into the gas phase. An example of sublimation is the disappearance of snow or frost without melting under certain conditions. #Step 4: Analyze the change in composition during sublimation#

Analyze the change in composition during sublimation

During the sublimation process, the substance (in this case, snow) does not undergo any changes in its chemical composition. The water molecules in the solid phase (ice) transition directly to the gas phase (water vapor), but the H2O molecules remain unchanged. #Step 5: Determine if sublimation is a physical or chemical change#

Determine if sublimation is a physical or chemical change

Since sublimation does not cause any changes in the chemical composition of the substance (snow), it can be classified as a physical change. In this process, only the state of the substance changes from the solid phase to the gas phase, while the chemical composition remains the same.