Kinetic Theory of Gases: Pressure, Volume, and Temperature Relationships
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Kinetic Theory of Gases
The kinetic theory explains that gas pressure depends on the volume of the container, the kinetic energy of the gas particles, and their temperature. This theory is fundamental to understanding all states of matter: solid, liquid, and gas.
Gas particles are very small and separated by large distances. They are in constant motion. Gases occupy the entire volume of their container and exert pressure on the container walls. This pressure results from the collisions of gas particles with the walls. The faster the gas particles move, the higher the temperature.
Boyle's Law
When a gas undergoes transformations at a constant temperature, the product of its pressure and volume remains constant (P x V = constant). This can be expressed as P1 x V1 = P2 x V2.
Kinetic Theory Explains Boyle's Law
At a constant temperature, the particles of a gas move at the same average speed. If the volume of the container is reduced, the particles collide with the walls more frequently, increasing the pressure. Conversely, if the volume increases, the particles travel further between collisions with the walls, resulting in lower pressure.
Kinetic Theory for Liquids and Solids
According to kinetic theory, matter consists of particles that are held together to varying degrees depending on the state of aggregation. Particles are in constant motion, with the freedom of movement varying by state. The faster the particles move, the higher the temperature of the substance.
State Changes
Changes of state are physical phenomena where the nature of matter does not change, only its state. These include:
- Sublimation (solid to gas)
- Fusion (solid to liquid)
- Vaporization (liquid to gas)
- Liquefaction or Solidification (gas to liquid or liquid to solid)
- Condensation (gas to liquid)
- Reverse Sublimation (gas to solid)
The melting point is the temperature at which a solid changes to a liquid throughout its mass. The boiling point is the temperature at which a liquid changes to a gas throughout its bulk.
State Changes Under Specific Conditions
The temperature at which a substance undergoes a state change depends on the surrounding conditions. An increase in external pressure raises the boiling point.
Difference Between Evaporation and Boiling
- Evaporation: The change of state from liquid to gas that occurs only on the surface of the liquid.
- Boiling: The change of state from liquid to gas that takes place throughout the bulk of the liquid.
Summary
- Gases and Kinetic Theory:
- Gases occupy the entire volume of their container.
- Gases exert pressure on the container walls.
- The faster particles move, the higher the gas temperature.
- Gas Laws:
- Boyle's Law: Relates pressure and volume at constant temperature.
- Gay-Lussac's Law: Relates pressure and temperature at constant volume.
- Charles's Law: Relates volume and temperature at constant pressure.
- Kinetic Theory and Other States of Matter:
Property Solid Liquid Gas Shape Constant Variable Variable Volume Constant Constant Variable Compressibility Not compressed Slightly compressed Easily compressed Expansion Not expand Expand Expand