Read Multi-Container Gas Problems One Container at a Time
Multi-container gas problems (connecting cylinders, mixed boxes, sublimation into a sealed vessel) collapse into PV=nRT applied separately to each container, then Dalton's law to combine partial pressures once everything shares one final volume.
A phase change alters the arrangement and motion of particles without creating a new substance.
Particles change their freedom of movement
Heat → particles move more freely
Heating increases particle motion: solid → liquid → gas. During a phase-change plateau, energy separates particles instead of raising temperature.
Connecting cylinders: conserve moles, not pressure
When valves between cylinders of different initial pressure and volume are opened, total moles of gas is conserved and redistributes to equalise pressure across the shared final volume
Comparing pressure, partial pressure and density across boxes
For boxes holding different particle counts of two gases, partial pressure of each gas depends only on its own mole count and the shared volume/temperature (Dalton's law) — density depends on total mass in that volume, a completely separate calculation from partial pressure.
Sublimation and Dalton's law in a sealed vessel
A solid subliming into a sealed vessel that already contains another gas adds its own partial pressure on top of the existing gas's partial pressure — total pressure is the sum, computed independently for each component via its own moles.
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- ✓Moles of gas are conserved when cylinders are connected — pressure re-equalises across the combined volume, moles do not change.
- ✓Partial pressure depends on that gas's own mole count in the shared volume; density depends on total mass, a separate quantity.
- ✓Dalton's law: total pressure = sum of each component's own partial pressure, computed independently.
Don't average initial pressures when cylinders are connected — average moles (weighted correctly by each cylinder's own PV=nRT), then recompute pressure from the combined volume.
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