This is defined as the ratio of the density of a gas to the density of dry air when both are measured at the same temperature and pressure. What is this quantity?

This is defined as the ratio of the density of a gas to the density of dry air when both are measured at the same temperature and pressure. What is this quantity?

• A. Relative Humidity
• B. Compressibility Factor
• C. Specific Gravity
• D. Viscosity Index

Answer: (C)

This quantity is the specific gravity of a gas relative to dry air. It’s defined as the ratio of the gas’s density to the density of dry air, measured at the same temperature and pressure. Since density for a gas at fixed T and P is proportional to its molar mass, this ratio is essentially the gas’s molar mass divided by the molar mass of air (about 29). So a gas heavier than air has a relative density greater than 1, while a lighter gas has a relative density less than 1. This concept is distinct from relative humidity, compressibility factor, or viscosity index, which refer to moisture content, non-ideal gas behavior, and temperature dependence of viscosity, respectively.

This quantity is the specific gravity of a gas relative to dry air. It’s defined as the ratio of the gas’s density to the density of dry air, measured at the same temperature and pressure. Since density for a gas at fixed T and P is proportional to its molar mass, this ratio is essentially the gas’s molar mass divided by the molar mass of air (about 29). So a gas heavier than air has a relative density greater than 1, while a lighter gas has a relative density less than 1. This concept is distinct from relative humidity, compressibility factor, or viscosity index, which refer to moisture content, non-ideal gas behavior, and temperature dependence of viscosity, respectively.