At constant pressure and molar mass, what happens to gas density when temperature increases?

At constant pressure and molar mass, what happens to gas density when temperature increases?

• A. Increases
• B. Decreases
• C. Remains the same
• D. Doubles

Answer: (B)

When you keep pressure and molar mass fixed, gas density is set by the relation density = PM/RT. This shows density is inversely proportional to temperature because the denominator has T. So as temperature increases, the density decreases. Intuitively, heating the gas at constant pressure makes it expand (volume increases). With more space for the same amount of mass, the mass per unit volume drops. The density cannot stay the same or increase under these conditions, since the volume expands with temperature while the amount of substance and the pressure remain constant.

When you keep pressure and molar mass fixed, gas density is set by the relation density = PM/RT. This shows density is inversely proportional to temperature because the denominator has T. So as temperature increases, the density decreases.

Intuitively, heating the gas at constant pressure makes it expand (volume increases). With more space for the same amount of mass, the mass per unit volume drops. The density cannot stay the same or increase under these conditions, since the volume expands with temperature while the amount of substance and the pressure remain constant.