Understanding Solid Carbon Dioxide: What is Dry Ice?

The question asks for the common name given to solid carbon dioxide. Let's explore what solid carbon dioxide is and its properties.

What is Solid Carbon Dioxide?

Carbon dioxide ($\text{CO}_2$) is a gas at standard room temperature and pressure. However, when cooled to a very low temperature (below -78.5 °C or -109.3 °F) at standard atmospheric pressure, it transitions directly from a gas to a solid state. This solid form of carbon dioxide is distinct from regular water ice.

Why is it Called Dry Ice?

The unique property of solid carbon dioxide is that it does not melt into a liquid when it absorbs heat at atmospheric pressure. Instead, it undergoes a process called sublimation, where it changes directly from a solid to a gas. Because it skips the liquid phase and doesn't produce any liquid water like regular ice melts, it is referred to as "dry ice".

• Regular water ice ($\text{H}_2\text{O}$ solid) melts into liquid water ($\text{H}_2\text{O}$ liquid). This is a solid-to-liquid phase transition (melting).
• Solid carbon dioxide ($\text{CO}_2$ solid) sublimes directly into gaseous carbon dioxide ($\text{CO}_2$ gas). This is a solid-to-gas phase transition (sublimation).

This lack of liquid formation makes it "dry" compared to water ice, hence the name dry ice.

Properties and Uses of Dry Ice

Dry ice is extremely cold and has several applications:

• Keeping items frozen, especially during transport, as it maintains a much lower temperature than water ice.
• Creating fog or smoke effects in theatrical productions or parties as the cold gas mixes with moist air.
• Industrial cleaning (dry ice blasting).

Analyzing the Options

Let's look at the given options in the context of solid carbon dioxide:

• Gas ice: This term is not a standard name for solid carbon dioxide. While it transitions to a gas, the solid form itself isn't typically called "gas ice".
• Wet ice: This term is often used casually to refer to regular water ice that is melting and producing liquid water, making things wet. Solid carbon dioxide does not produce liquid, so this is incorrect.
• Solid ice: This could potentially refer to any substance in its solid state that is typically a liquid or gas at room temperature and is frozen, but it's not the specific common name for solid carbon dioxide. Water ice is "solid ice" but specifically water in solid form.
• Dry ice: As explained above, this is the widely accepted and common name for solid carbon dioxide due to its property of sublimating directly into a gas without forming a liquid.

Based on the properties and common terminology, dry ice is the correct answer for solid carbon dioxide.

Revision Table: Key Concepts

Additional Information on Dry Ice and Phases

The phase of a substance (solid, liquid, or gas) depends on both temperature and pressure. While water transitions through solid (ice), liquid (water), and gas (steam) phases at standard atmospheric pressure, carbon dioxide behaves differently. At atmospheric pressure, it only exists as a solid or a gas. The liquid phase of carbon dioxide can only exist at pressures significantly above atmospheric pressure (specifically, above its triple point pressure of 5.18 atm).

The triple point is the temperature and pressure at which the three phases (solid, liquid, and gas) of a substance coexist in equilibrium. For carbon dioxide, the triple point is at -56.6 °C and 5.18 atm. Below this pressure, solid $\text{CO}_2$ will always sublime directly to gas when heated.