Five moles of an ideal gas at 293   K is expanded isothermally from an initial pressure of 2 . 1   MPa to 1 . 3   MPa against at constant external pressure 4 . 3   MPa . The heat transferred in this process is ___ kJmol - 1 . (Rounded-off to the nearest integer) [ Use R = 8 . 314   J   mol - 1   K - 1 ]

Step-by-step solution

n = 5 ,   T = 293   K = const , ΔU = 0 P 1 = 2 . 1   MPa , P 2 = 1 . 3   MPa P ext = 4 . 3   MPa = const . W = - P ext V 2 - V 1 = - P ext nRT P 2 - nRT P 1 or, W = - P ext nRT 1 P 2 - 1 P 1 = - 4 . 3 × 5 × 8 . 314 × 293 1 1 . 3 - 1 2 . 1 = - 4 . 3 × 5 × 8 . 314 × 293 2 . 1 - 1 . 3 1 . 3 × 2 . 1 = - 15347 . 7   J or, W = - 15 . 35   kJ Δ U 0 = q + W ∴     q = - W or, q = 15 . 35   kJ (for 5 moles) ∴   &#1