# What happens to the density of a gas as its volume decreases at constant pressure and temperature?

Question: What happens to the density of a gas as its volume decreases at constant pressure and temperature?

When the volume of a gas decreases while maintaining constant pressure and temperature, the density of the gas increases. This is because density is defined as the mass per unit volume. As the volume decreases, the same amount of mass occupies a smaller space, leading to an increase in density. This relationship is described by Boyle's Law for ideal gases, which states that the product of pressure and volume is constant for a given mass of confined gas at constant temperature. Therefore, if the volume decreases, the pressure must remain constant, and the density of the gas must increase to maintain the balance in the equation \( PV = nRT \), where \( P \) is pressure, \( V \) is volume, \( n \) is the number of moles, \( R \) is the universal gas constant, and \( T \) is temperature.