The density of air in a sealed container is measured at different temperatures while the container volume stays constant. Temperature / °C Density / kg/m³ 0...
Question 1 Report
The density of air in a sealed container is measured at different temperatures while the container volume stays constant.
| Temperature / °C | Density / kg/m³ |
|---|---|
| 0 | 1.29 |
| 50 | 1.09 |
| 100 | 0.95 |
| 200 | 0.75 |
The container has a small valve that releases gas when pressure exceeds 101 kPa. Why does the density fall as temperature rises?
Answer Details
The container has a fixed volume, but it also has a pressure-release valve that opens whenever the internal pressure exceeds 101 kPa. As the air is heated, the molecules gain kinetic energy and move faster, creating more frequent and harder collisions with the container walls. This raises the pressure above 101 kPa, causing the valve to open and allow some gas molecules to escape.
Once molecules leave, the total mass of gas inside the container decreases. Since density equals mass divided by volume, and the volume stays constant while the mass falls, the density must decrease. Each time the temperature is raised further, more molecules escape through the valve, reducing the mass and hence the density even more.
The container does not expand (it is described as having constant volume). Individual molecules do not shrink when heated - in fact, molecular size is essentially unchanged by temperature. Molecules speed up at higher temperatures, not slow down.
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