How do I predict whether a gas is heavier or lighter than air?

I have been looking for a table that lists which gases are heavier or lighter than air. I have not found one. I want to know whether natural gas, propane and butane are lighter than air. Ben 10/09/99

	Vocabulary
	density ideal gas molar mass molar volume

The density of a gas is roughly proportional to its molecular weight. Air has an average molecular weight of about 29 g/mol, so any gas with a molecular weight heavier than that will be denser than air.

Propane (C₃H₈) and butane (C₄H₁₀) have molecular weights of 44 and 58 g/mol, respectively, so both will be heavier than air.Natural gas is a mixture, not a compound, and its composition varies considerably depending on its source. The natural gas delivered to consumers in the U. S. is about 95% methane (CH₄, molecular weight 16 g/mol) with the remainder being mostly ethane, propane, and carbon dioxide. A balloon filled with natural gas rises in air, although it doesn't have the lift a helium balloon has.

Author: Fred Senese senese@antoine.frostburg.edu

General Chemistry Online! How do I predict whether a gas is heavier or lighter than air?