The gas constant, R, has the value 8.3145 J K–1 mol–1; 1 bar is 105 N m–2; 1 atmosphere is 1.01325 × 105 N m–2.
4 × 10-3 moles of an ideal gas are held inside a cylinder by a piston such that the volume of the gas is 10 cm3; the whole assembly is held in a thermostat at 298 K.
(a) Calculate the pressure of the gas in N m–2. [Note that the SI unit of volume is m3.]
(b) Assume that the external pressure is fixed at 1 bar. Explain why the piston moves out when it is released, and why it eventually comes to a stop. What will the pressure of the
gas inside the cylinder be when the piston finally stops?
(c) Calculate the volume of the gas inside the cylinder when the piston has come to rest and hence the work for this irreversible expansion.
(d) State the change in the internal energy, ΔU, of the gas when it undergoes this isothermal expansion. Hence, using the First Law, calculate the heat associated with the
expansion, explaining its sign.
(e) Calculate the work associated with reversible isothermal expansion between the same initial and final states as the irreversible expansion described above; hence find the
heat. Comment on these values in relation to those for the irreversible expansion.
(f) Determine the enthalpy change of the gas in (i) the reversible and (ii) the irreversible expansion.
