Which statement best explains why diffusion is faster in a gas than in a liquid or solid?

Which statement best explains why diffusion is faster in a gas than in a liquid or solid?

• A. Gas particles are heavier
• B. Gases have stronger intermolecular forces
• C. Gases are incompressible
• D. Gas particles move faster and are farther apart

Answer: (D)

Diffusion rate is driven by how fast particles move and how easily they can spread out to fill space. In a gas, particles zip around with high speeds because they have lots of kinetic energy and there are very weak attractions between them. They sit far apart from each other, so the average distance a particle travels before hitting another (the mean free path) is large. That means a lot of mixing can happen quickly as particles move from regions of high concentration to low concentration over long, unobstructed journeys. In liquids and especially solids, particles are packed much more tightly and feel stronger intermolecular forces. That limits how freely they can move, slowing down the spread of particles from one area to another. Solids, in particular, have particles essentially fixed in place with only small vibrations, making diffusion very slow; liquids allow more movement but still not as free as gases. So the key idea is that gases combine high particle speeds with large spacing, giving both a high mobility and easy access to different regions of space, which speeds up diffusion compared with liquids or solids. The statements about heavier particles, stronger intermolecular forces, or incompressibility don’t explain the faster diffusion in gases; gases are actually more compressible and have weaker intermolecular forces, and speed depends more on kinetic energy than mass alone.

Diffusion rate is driven by how fast particles move and how easily they can spread out to fill space. In a gas, particles zip around with high speeds because they have lots of kinetic energy and there are very weak attractions between them. They sit far apart from each other, so the average distance a particle travels before hitting another (the mean free path) is large. That means a lot of mixing can happen quickly as particles move from regions of high concentration to low concentration over long, unobstructed journeys.

In liquids and especially solids, particles are packed much more tightly and feel stronger intermolecular forces. That limits how freely they can move, slowing down the spread of particles from one area to another. Solids, in particular, have particles essentially fixed in place with only small vibrations, making diffusion very slow; liquids allow more movement but still not as free as gases.

So the key idea is that gases combine high particle speeds with large spacing, giving both a high mobility and easy access to different regions of space, which speeds up diffusion compared with liquids or solids. The statements about heavier particles, stronger intermolecular forces, or incompressibility don’t explain the faster diffusion in gases; gases are actually more compressible and have weaker intermolecular forces, and speed depends more on kinetic energy than mass alone.