Question

Explain why solid \(\mathrm{CO}_{2}\). is referred to as dry ice.

Short answer

Solid \r\(\rmathrm{CO}_{2}\r)\) is called dry ice because, unlike water ice, it sublimates directly from a solid to a gas without leaving any liquid, hence it remains 'dry' during the transition.

Step-by-step solution

Defining Dry Ice

Understand that solid carbon dioxide (\r\(\rmathrm{CO}_{2}\r)\)) is commonly called dry ice. This name is derived from its appearance and some of its physical properties.

Analyzing Physical Properties

Explore the physical properties of solid \r\(\rmathrm{CO}_{2}\r)\). Unlike water ice, which melts into a liquid at temperatures above 0 degrees Celsius (\r\(0^{\rcirc}\r)\)C), solid \r\(\rmathrm{CO}_{2}\r)\) does not melt at standard atmospheric pressures. Instead, it undergoes sublimation, meaning it transforms directly from a solid to a gas at temperatures above -78.5 degrees Celsius (\r\(-78.5^{\rcirc}\r)\)C).

Understanding the Term 'Dry'

Evaluate why the term 'dry' is applied to dry ice. Since solid \r\(\rmathrm{CO}_{2}\r)\) sublimates rather than melts, it doesn't leave any wet residue that is typically associated with the melting of water ice. Thus, because it transitions from solid to gas without going through the liquid phase, it is called 'dry' ice.

Key concepts

Sublimation

Sublimation is a fascinating process where a substance transitions from a solid to a gas without passing through the intermediate liquid state. This interesting phenomenon is exactly what happens with dry ice, which is the solid form of carbon dioxide (CO₂). Imagine placing a block of dry ice in a room temperature environment; instead of melting, it appears to 'vanish' into thin air as it becomes a gas.

This direct change is caused by an increase in molecular energy as the dry ice gains heat. When the molecules gain enough energy, they break free from their solid structure and disperse as a gas. Sublimation occurs under certain conditions of temperature and pressure. For CO₂, this occurs at temperatures above -78.5 degrees Celsius (-109.3°F), often making for dramatic effects as the gas forms clouds of fog when it interacts with warmer air.

Physical Properties of CO2

Carbon dioxide (CO₂) is more than just a gas; it has several intriguing physical properties that define its behavior under different conditions. First and foremost, CO₂ is a colorless and odorless gas at room temperature. It is also non-flammable and slightly acidic in water, leading to carbonic acid, which is why it's found in carbonated beverages.

The solidity of CO₂, known as dry ice, showcases its uniqueness. At atmospheric pressure, dry ice maintains its solid form up to -78.5°C, and upon reaching this temperature, it sublimates. CO₂ has a density of approximately 1.98 kg/m³ at standard temperature and pressure, making it heavier than air. In its solid state, it has a density of around 1,500 kg/m³, which is why it sinks in air and creates that mysterious fog effect when used in entertainment or transportation to keep goods cold without the mess of melting ice.

Solid Carbon Dioxide

Solid carbon dioxide, commonly known as dry ice, distinguishes itself from regular water ice by its temperature and how it interacts with its environment. Dry ice is extremely cold with a surface temperature of -78.5°C, which makes it very effective at freezing and keeping things frozen because it is much colder than water ice. Handling it requires insulated gloves to prevent frostbite.

The utility of dry ice extends to various applications, from shipping perishables to creating atmospheric effects on stage or for Halloween decorations. Since dry ice sublimates, it leaves behind no liquid, a property that makes it particularly useful in situations where moisture could cause damage or contamination. The 'dry' aspect of dry ice is crucial for preserving electronic components, medical specimens, or food items during transport, as it avoids the risk of water damage.