The kinetic-molecular theory is based on the principles that particles of matter are always moving. The kinetic-molecular theory provides a model of the ideal gas. An ideal gas is an imaginary gas that fits all the assumptions of the kinetic-molecular theory.
- Gases consist of large numbers of tiny particles that are far apart in relation to their size. This accounts for their lower denisty and their ability to be compressed easily.
- Collisions between gas particles and between particles and container walls are elastic. An elastic collision is one where their is no net loss of kinetic energy, only a transfer of energy between particles when the temperature is constant.
- Gas particles are in constant motion, therefore they have kinetic energy.
- There are no forces of attraction or repulsion between gas particles, therefore when gases collide they do not stick together, but immediately bounce apart.
- The average kinetic energy of gas particles depends on the temperature of the gas. All gases at the same temperature have the same kinetic energy.
The kinetic-molecular theory of gases as stated above only applies to ideal gases. In the real world although ideal gases do not exist, some gases behave almost ideally when the surrounding conditions are correct. The above assumptions of the kinetc molecular theory account for the physical properties of gases.
- Expansion
Gases do not have a definite shape or volume, therefore they take the shape of their container and their volume.
- Fluidity
Gas particles lack forces which would attract them to each other so they easily glide past each other. Their ability to flow is similar to liquids, therefore they are considered fluids.
- Low Density
The density of a substance in the gas state is lower then the substance in other states because a gas’s particles are far apart.
- Compressibility
Gases compress well because there is so much empty space between them initially. When you compress an object, you remove the empty space. Therefore gases have a high compressibility because so much empty space is between them.
- Diffusion
Diffusion is the instant mixing of particles caused only by their random motion. Gases diffuse easily because their random and continuous motion carries them through the air. The rate of diffusion depends on the gas particles’s speeds, diameters, and attractive forces between them.
- Effusion
Effusion is the process where gas particles under pressure pass through a tiny opening. The rates of effusion are proportional to the velocities of their particles.
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