In a liquid, particles are held close together by cohesive forces. These forces are strong enough to keep the liquid particles from moving past each other, giving a liquid a definite shape and volume. In contrast, the cohesive forces between particles in a gas are much weaker. This allows gas particles to move more libremente past each other, and the gas to expand to fill any container.

The difference in particle movement between liquids and gases is due to the difference in their molecular structures. Liquids are composed of molecules that are closely packed together, while gases are composed of molecules that are widely spaced apart. The close proximity of the molecules in a liquid creates strong cohesive forces between them, while the wide spacing of the molecules in a gas creates weak cohesive forces.

The strength of the cohesive forces in a liquid is also affected by the temperature of the liquid. As the temperature of a liquid increases, the average kinetic energy of the liquid particles also increases. This increase in kinetic energy causes the liquid particles to move faster and more randomly, which weakens the cohesive forces between them. As a result, a liquid becomes less viscous and more like a gas as its temperature increases.

In summary, the particles in a gas move more freely than the particles in a liquid due to the weaker cohesive forces between the particles in a gas. The weaker cohesive forces in a gas are due to the wide spacing of the molecules in a gas compared to the close proximity of the molecules in a liquid.