Asteel cylinder with a moveable piston on top is filled with helium (he) gas. the force that the piston exerts on the gas is constant, but the volume inside the cylinder doubles, pushing the piston up. which of the following answers correctly states the cause for the change described in the scenario? the temperature increased. the density of the helium atoms decreased. the pressure decreased. the helium atoms increased in size.

Assuming that Helium behaves as an ideal gas, that means that the Helium molecules have no intermolecular forces. They move freely without depending on one another's energy. We can use the ideal gas equation:

PV = nRT, where

P = pressure
V = volume
n=number of moles of gas
R = gas constant equal to 8.314 J/mol-K
T = absolute temperature

If pressure is kept constant, and we assume that the system is closed such that no moles are added or escaped, then the equation becomes

P/nR = T/V = k, where the k denotes constant. Therefore,

T = kV

So, when the volume doubles, the only reason for this is the increase also of temperature. This is because temperature is directly proportional to the volume of the gas. The answer is: The temperature increased. 

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