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.

Answer 1

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