A 19.0-L volume of an ideal gas in a cylinder with a piston is at a pressure of
ID: 704027 • Letter: A
Question
A 19.0-L volume of an ideal gas in a cylinder with a piston is at a pressure of 2.8 atm. Enough weight is suddenly removed from the piston to lower the external pressure to 1.4 atm. The gas then expands at constant temperature until its pressure is 1.4 atm.
Find the change in enthalpy, ?H, for this change in state.
Express your answer using two significant figures.
Find the heat, q, associated with this change in state.
Express your answer using two significant figures.
Find the work, w, associated with this change in state.Part D
Express your answer using two significant figures.
Explanation / Answer
volume of an ideal gas = 19 L
Pressure P1 = 2.8 atm
external pressure P = 1.4 atm
expands at constant temperature dT = 0
pressure P2 = 1.4 atm
Final volume V2 = P1V1/P2
= 2.8 x 19 / 1.4 = 38 L
Work done W = - P (V2 - V1)
= - 1.4 x (38 - 19) = - 26.6 L-atm x 101.3 J/L-atm
= - 2691.92 J = - 2.7 kJ
Change in internal energy at constant temperature
dU = 0
From the first law of thermodynamics
dU = Q + W
Q = - W = 2691.92 J = 2.7 kJ
for an ideal gas Enthalpy change ?H = 0
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