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An ideal gas undergoes a reversible adiabatic expansion in a piston-cylinder system. The initial pressure is \mathrm{4.0 \: atm,} and the initial volume is \mathrm{40 \: liters}. During the expansion, the volume increases to \mathrm{80 \: liters}. Calculate the final pressure of the gas.

Given the heat capacity ratio \mathrm{(Cp/Cv)} for the gas is 1.25.

Option: 1

\mathrm{3\: atm}


Option: 2

\mathrm{4\: atm}


Option: 3

\mathrm{2\: atm}


Option: 4

\mathrm{2.5\: atm}


Answers (1)

best_answer

Given data:

Initial pressure \mathrm{\left(P_i\right)=4.0 \mathrm{~atm}}

Initial volume \mathrm{\left(V_i\right)=40\: liters}

Final volume \mathrm{\left(V_f\right)=80\: liters}

Heat capacity ratio \mathrm{\left(C_p / C_v\right)=1.25}

For a reversible adiabatic process, the relationship between initial and final conditions is given by:

\mathrm{ P_i \cdot V_i^\gamma=P_f \cdot V_f^\gamma }
Solving for the final pressure \mathrm{ \left(P_f\right) : }

\mathrm{ P_f=\frac{P_i \cdot V_i^\gamma}{V_f^\gamma} }

Substituting the values and solving:

\mathrm{ P_f=\frac{(4.0 \mathrm{~atm}) \cdot(40 \text { liters })^{1.25}}{(80 \text { liters })^{1.25}} \approx 2.00 \mathrm{~atm} }

Therefore, the final pressure of the gas is approximately \mathrm{ 2.00 \mathrm{~atm} }

So, the correct option is 3.

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