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Home Concept Builders Gases and Gas Laws Pressure Concepts Help Help 3

Pressure Concepts - Questions 3 Help

A sample of gas has a pressure due to the collisions of moving gas particles with the container walls. This pressure can be understood at the particle level. Each collision of a gas particle with the container wall results in a force on the wall. Because there are so many particles colliding so frequently with the container wall, there is enough force that accumulates to result in a noticeable pressure. Any variable that effects the ratio of the cumulative amount of force per unit of wall area will effect this pressure.

There are two very similar versions of questions in this Question Group. One of the versions is shown below.
 

Version 1:
Container A and Container B are the same size; their volume and surface area is the same. They contain the same type of gas and the same number of particles of gas. But the particles in Container A are moving faster (on average) than the particles in Container B. Which container will have the greatest gas pressure?

Gases push! They push outward upon the walls of the container that contains them. And this pushing is the result of collisions. Each collision of a gas particle on a container wall contributes to an overall amount of force on the wall. By definition, the pressure is the total force divided by the area of the container walls. So to maximize pressure, this ratio of force per area would have to be maximized. The larger the ratio ... the larger the pressure.

So exactly how can this ratio of force per area be maximized. Of the two components of the pressure ratio, the area is easiest to explain. Making the area as small as possible makes the pressure as large as possible.

The force component of this ratio is more difficult to explain. But to keep it simple, the pressure is maximized if the overall and total forcefulness of the collisions of gas particles with container walls is increased. The forcefulness of the collisions can be increased by collisions that ...
 
  • occur at greater speeds.
  • involve more massive particles (assuming the same or greater speed).
  • involve more particles doing the colliding rather than less particles.
  • occur more frequently (either because there are more particles or the particle speed is faster and they can traverse the distance from wall to wall in less time).

In this question, all variables (container wall area, mass of particles, and number of particles) are the same for the two containers with the exception of the particle speed. The pressure will be greater for greater average particle speed. Collisions of faster particles with the container wall are more forceful collisions. They will also occur more frequently since the particles will traverse the distance from wall to wall in less time.
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