3 Intermolecular spaces

Experiment.

• Hold a beaker full of ammonia gas (NH₃) upside down over a beaker of hydrogen chloride gas (HCl) (with a cover separating them, which is then removed).
• A white cloud of ammonium chloride (NH₄Cl) forms and spreads until it fills both beakers.

Explanation.

• HCl molecules, although heavier (denser), rise upward through the spaces between ammonia molecules; NH₃ molecules, although lighter, move downward through the spaces between HCl molecules.
• Where they meet, they combine to form NH₄Cl, which diffuses to fill both beakers.

Conclusion.

• There are relatively large spaces between gas molecules (intermolecular spaces).
• This also explains why gases are easily compressed: pressure pushes the molecules closer together, so the volume decreases.