Consider a sample of helium gas in a container fitted with a piston, as pictured below. The piston is frictionless, but has a mass of 10.0 kg. How many of the following processes will cause the piston to move away from the base and decrease the pressure of the gas

Question:

Consider a sample of helium gas in a container fitted with a piston, as pictured below. The piston is frictionless, but has a mass of 10.0 kg. How many of the following processes will cause the piston to move away from the base and decrease the pressure of the gas? Assume ideal behavior.

I.

heating the helium

II.

removing some of the helium from the container

III.

turning the container on its side

IV.

decreasing the pressure outside the container

Two of the following processes will cause the piston to move away from the base and decrease the pressure of the gas.

III and IV.

III.

turning the container on its side

IV.

decreasing the pressure outside the container

Explanation:

To answer the question, we will be required to analyze each option as follows

I.  

heating the helium

Here, assuming ideal behavior, according to Charles' law, at constant pressure the volume of a given mass of gas is directly proportional to its temperature, in  Kelvin.

Therefore, heating the helium will increase the volume of the gas and move up the piston to move away from the base. However the pressure will remain constant.

Only one condition is met

II.

removing some of the helium from the container

If the container is empty, the piston ill rest on the base of the container.

Does not meet the conditions.

III.

turning the container on its side

Here, the force of the piston on the helium gas due to grvity is removed, therefore the helium will expand and the pressure of the helium gas will be reduced as the force of the piston is no longer in effect, the volume  occupied by the gas increases, therefore the piston moves away from the base.

Both conditions are met.

IV.

decreasing the pressure outside the container

When the pressure outside the container is decreased the force due to atmospheric pressure is reduced and the helium will expand to assume a lesser equilibrium pressure while moving the piston away from the base.

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