Which gas diffuses faster

Process of diffusion

Matter is constantly in motion

The fact that matter is constantly in motion can best be observed with liquids, just think of a mountain stream or the surf of the seashore, and the water from the pipe, like pig iron from the blast furnace, always flows to a lower point. Solid bodies can also be in motion, such as the second hand of the clock, the boulders in a rock fall or frozen water falling from the sky in the form of snow.

That there are also gases in motion can be indirectly observed when twigs and branches move in the wind and thus allow conclusions to be drawn about the strength of the air movement. Bad smells, like the scent of a bouquet of flowers, vanish when you open the window.

If you bring two gases into a closed space, their concentrations will completely equalize each other after a sufficient time and they penetrate each other. Over time, this leads to complete mixing due to the even distribution of the particles involved. The particles can be atoms, molecules or charge carriers. The substances are mostly gases and liquids, rather than solids.




The appearance of diffusion

If hydrogen is passed into a plastic bag (experiment 1), the particles of hydrogen displace the particles of air. In experiment 2, too, the particles of carbon dioxide displace the particles of air from the beaker. One observes different readings on the scales, whereby one can claim that hydrogen is lighter than air and that carbon dioxide is heavier than air.

If one observes the experiment for a longer period of time, one notices that the display of the balance changes again until the original equilibrium is restored. Obviously, the hydrogen particles do not stay in the container for very long and move out again against gravity. Now the air particles can penetrate again.

Air, hydrogen and carbon dioxide have their own movement called heat movement. This allows them to spread freely in the room. The behavior of substances to mix with one another is called diffusion (Latin for spreading, dispersing).

The behavior of diffusion can also be observed in liquids (experiment 3). Even if you don't stir your coffee with the sugar, it will taste evenly sweet after a while. However, diffusion in liquids is much slower than in gases. Diffusion processes can also be observed in solid bodies (Exercise 6)


Different speed of diffusion

As experiment 5 shows, gases can also easily pass through porous walls. This can be explained if one assumes a different diffusion speed of air and hydrogen. It is difficult for the air particles to leave the clay cell, but the hydrogen particles move very quickly through the clay wall. There is overpressure inside the clay cell. If you remove the beaker after a while, the particles of hydrogen diffuse fastest through the wall to the outside. Now there is a negative pressure in the cell and air is sucked in through the tube.