Question

Calculate the constant external pressure needed to compress an ideal gas from 25 dm³ to 15 dm³. The amount of work done in the compression process is 3500 joules.

Answer 1

As the compression of the gas takes place against a constant pressure, the work done is given by

W = -P_ex (V₂ – V₁)

W = Work done by the gas against the external pressure = 3500 J

∴ W = \(\frac{3500}{100}\) = 35 dm³ bar

P = Constant external pressure = ?

V₂ = Final volume = 15 dm³

V₁ = Initial volume = 25 dm³

∴ 35 = -P × (15 – 25)

∴ 35 = 10 × P

∴ P = \(\frac{35}{10}\) = 3.5 bar

∴ External pressure = 3.5 bar