Carbon Dioxide (CO₂) — Properties, Uses & Safety

Overview

Carbon dioxide (CO2) is a colorless, odorless gas with a molar mass of 44.01 g/mol, composed of one carbon atom double-bonded to two oxygen atoms in a linear molecular geometry. At standard temperature and pressure, CO2 exists as a gas and is present in Earth's atmosphere at approximately 0.04% (about 420 ppm as of recent measurements). Carbon dioxide is the primary anthropogenic greenhouse gas driving climate change — human activities such as burning fossil fuels, deforestation, and cement production have increased atmospheric CO2 levels by over 50% since pre-industrial times. Despite its role in global warming, CO2 is essential for life on Earth. Plants use it in photosynthesis (6 CO2 + 6 H2O -> C6H12O6 + 6 O2) to produce glucose and oxygen, forming the foundation of nearly all food chains. CO2 is also used commercially to carbonate beverages, as a refrigerant in its solid form (dry ice, which sublimes at -78.5 degrees C), in fire extinguishers, and as a supercritical fluid solvent for decaffeinating coffee. The GHS hazard code H280 classifies compressed CO2 as a gas under pressure. While not toxic at low concentrations, elevated CO2 levels above 5% can cause headaches, dizziness, and asphyxiation by displacing oxygen. For chemistry students, carbon dioxide is a cornerstone compound connecting multiple curriculum topics. Its linear geometry and nonpolar nature despite having polar C=O bonds perfectly illustrate VSEPR theory and the concept of molecular polarity versus bond polarity. The CO2 molecule demonstrates how symmetry can cancel out individual bond dipoles. Carbon dioxide's role in the carbon cycle, ocean acidification (CO2 + H2O -> H2CO3), combustion reactions, and photosynthesis makes it central to discussions of chemical equilibrium, acid-base chemistry, and environmental science.

IUPAC Name

carbon dioxide

CAS Number

124-38-9

PubChem CID

280

Molecular Formula

CO₂

Molar Mass

44.01 g/mol

State at STP

gas

Appearance

Colorless, odorless gas