How much heavier than air is chlorine gas at room temperature?

Chlorine gas is indeed approximately 2.5 times heavier than air at room temperature. This is because the molar mass of chlorine (Cl₂) is about 70.9 g/mol, while the average molar mass of air, primarily composed of nitrogen (78%) and oxygen (21%), is around 28.8 g/mol.

When assessing the relative density of gases, a value greater than 1 indicates that the gas is heavier than air, which is the case with chlorine. The value of approximately 2.5 suggests that chlorine gas will tend to settle in low-lying areas and can pose a hazard in such environments. Understanding this property of chlorine is crucial for safety in handling and using this gas, particularly in water treatment facilities where chlorine is commonly used for disinfection.