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# A sample of helium gas, He(g), is placed in a rigid cylinder sealed with a movable piston. The tempe

NY Regents Chemistry Exam Jan 2023

A sample of helium gas, He(g), is placed in a rigid cylinder sealed with a movable piston. The temperature of the helium is 25.0°C. The volume of the helium is 300. milliliters and the pressure is 0.500 atmosphere.

58 State, in terms of the average distance between the helium atoms, why the density of the gas increases when the piston is pushed farther into the rigid cylinder. 

Density is equal to mass over volume. When the piston is pushed further, volume decreases and the average distance between helium atoms decreases as well. This results in an increased density of the gas.

Answer: The average distance between helium atoms decreases which results in the increased density of the gas.

59 Determine the volume of the helium gas when the pressure is increased to 1.50 atm and the temperature remains at 25.0°C. 

Table T on the Reference table gives an equation for gases which is (P1V1)/T1 = (P2V2)/T2

Since the temperature remains the same, we can cancel it from the equation and get P1V1 = P2V2

P1 = 0.500 atm from the passage on top

V1 = 300. milliliters from the passage on top

P2 = 1.50atm

V2=?

(0.500 atm )(300. ml) = (1.50atm)(V2)

60 Compare the number of helium atoms in the cylinder at a pressure of 0.500 atm to the number of helium atoms in the cylinder when the pressure is increased to 1.50 atm by pushing the piston in. 

Increasing pressure has no effect on the number of helium atoms. The only thing that would change the number of helium atoms would be if more atoms were added or some atoms were taken out of the container.

Answer: The number of atoms did not change.