What describes a gas?

A gas is characterized by its lack of definite shape and volume. This means that gases will expand to fill the container they are placed in, taking the shape of that container without being constrained by fixed boundaries. The particles in a gas are in constant, rapid motion, moving freely and independently of one another. This fast movement contributes to their ability to spread out and fill any available space.

In addition to these properties, gases are also compressible, which is an important characteristic. However, the defining features of a gas are fundamentally its lack of shape and volume, alongside the rapid motion of its particles. This clear understanding of the nature of gases is foundational in differentiating them from solids and liquids, which have definable shapes and volumes.