I can't take this Heat!

A system consists of two chambers, one is filled with a gas of molecules $$(P_o,V_o,T_o)$$ while, the other chamber is vacuum. The Piston is held by a spring.

Find the heat capacity $$\displaystyle C$$(in J/K) of the system, such that when the gas is released, the piston touches the right wall and the spring is relaxed.

Details and Assumptions:
$$\bullet$$ The gas is Monoatomic in nature.
$$\bullet$$ $$\displaystyle P_o = 1.5 atm$$
$$\bullet$$ $$\displaystyle V_o = 3.5 L$$
$$\bullet$$ $$\displaystyle T_o = 227^oC$$
$$\bullet$$ $$\displaystyle k = 150 N/m$$

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