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# Why does a gas in a closed container exert pressure?

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According the kinetic molecular theory, gas in a closed container exerts pressure on the walls of that container because its molecules are in constant motion, which causes some molecules to impact the walls. The more the gas molecules impact the walls of the container, the greater the pressure.

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The amount of pressure a gas exerts on a closed container is related both to the mass of the gas in the container and the temperature of that gas. The mass of gas matters because that determines how many molecules are in the container. The more molecules there are, the more often molecules will strike the walls. Temperature causes the gas molecules to move more quickly, which also increases the rate. A decrease in the volume of the container also increases the pressure of the gas.

Pressure is the amount of force one substance exerts on another substance for each unit of area. If it is within an atmosphere, the air outside of a container constantly exerts pressure as well. A balloon will only inflate if the pressure of the gas put into it is greater than the atmospheric pressure around it. On Earth, the average air pressure at sea level is 14.7 pounds per square inch.

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## Related Questions

• A:

In a given container, billions of particles of gas are constantly moving around randomly, colliding with the sides of the container. With thousands of collisions per second, individual collisions do not register, but an average that amounts to a constant force known as the pressure of gas.

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Gas is easier to compress than liquid because liquid must fit within a fixed volume, while gaseous molecules and atoms can spread out an infinite distance. The comparatively greater space available between gas molecules and atoms makes compression much simpler.

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The three factors that affect gas pressure are the number of gas molecules, the volume of the container and the temperature of the container that contains the gas. If there are two equal-sized containers, and one contains double the amount of gas molecules, this container has a higher gas pressure.