Why do gases exert pressure?

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1. Gases are composed of a large number of molecules that are in constant, random motion. These molecules are moving in all directions and at different speeds.
2. When these gas molecules collide with the walls of their container, they exert a force on the walls. This is because, according to Newton's second law of motion, a force is exerted when an object (in this case, a gas molecule) changes its momentum (which happens when it collides with the wall and changes direction).
3. The pressure exerted by a gas is the force that the gas molecules exert per unit area of the container's walls. It is the result of billions of collisions of gas molecules with the walls.
4. The more molecules in a given volume or the faster they are moving, the more collisions occur and the greater the pressure. This is why increasing the temperature (which increases the speed of the molecules) or the number of molecules in a container increases the pressure.
5. Thus, gases exert pressure due to the constant, random motion of their molecules and the collisions of these molecules with the walls of their container.

Key Concepts

Kinetic Molecular Theory

The Kinetic Molecular Theory explains the behavior of gases in terms of the motion of their particles. It posits that gas particles are in constant, random motion and that they collide with each other and the walls of their container. These collisions result in pressure, as the force exerted by the particles on the walls of the container is what we measure as gas pressure.

Pressure Definition

Pressure is defined as the force exerted per unit area. In the context of gases, it is the result of countless collisions of gas molecules with the surfaces of their container. The greater the number of collisions and the higher the energy of the particles, the greater the pressure exerted by the gas.

Temperature and Pressure Relationship

The relationship between temperature and pressure in gases is described by Gay-Lussac's Law, which states that the pressure of a gas is directly proportional to its absolute temperature when volume is held constant. As temperature increases, gas particles move faster, leading to more frequent and forceful collisions with the container walls, thereby increasing the pressure.