How is gas pressure defined in terms of molecular movement?

• A. Only as the weight of the gas
• B. Sum of forces due to collisions of molecules
• C. Average speed of gas molecules
• D. Volume of gas divided by its temperature

Answer: (B)

Gas pressure is defined as the sum of forces resulting from collisions of gas molecules with the walls of a container. In a gas, molecules are in constant motion and travel in straight lines until they collide with each other or with the surfaces around them. Each collision exerts a force on the surface, and when considering a large number of molecules, the cumulative effect of all these microscopic collisions results in what we perceive as gas pressure.

Understanding gas pressure in this way highlights the relationship between molecular movement and pressure. The faster the molecules move, the more frequently and forcefully they collide with the container walls, thereby increasing the pressure. This concept is central to the kinetic theory of gases, which relates molecular activity to macroscopic properties such as pressure and temperature.

The other options do not accurately encapsulate the complexity of gas pressure. The weight of the gas, average speed of the molecules, or a ratio of volume to temperature fails to account for the dynamic nature of molecular collisions that fundamentally defines pressure.