版权所有：华东理工大学物理化学教研室 16 When the system expands through a distance dz against pex, the work done: dw = - pex A dz where Adz is the change in volume, dV, in the course of the expansion. 1). The general expression for work the area of the piston, A the external pressure, pex the force on the outer face, F =pex A. 2.3 Expansion work
版权所有：华东理工大学物理化学教研室 16 When the system expands through a distance dz against pex, the work done: dw = - pex A dz where Adz is the change in volume, dV, in the course of the expansion. 1). The general expression for work the area of the piston, A the external pressure, pex the force on the outer face, F =pex A. 2.3 Expansion work
版权所有：华东理工大学物理化学教研室 17 The work done when the system expands by dV against a pressure pex is 1). The general expression for work dw = −Fdz = − pex dV ∫ = − fi d ex VV w p V The total work done, w: 2.3 Expansion work
版权所有：华东理工大学物理化学教研室 17 The work done when the system expands by dV against a pressure pex is 1). The general expression for work dw = −Fdz = − pex dV ∫ = − fi d ex VV w p V The total work done, w: 2.3 Expansion work
版权所有：华东理工大学物理化学教研室 18 In general, the work done on a system can be expressed in the form dw = -Fdz, where F is a 'generalized force and dz is a 'generalized displacement'. V C ϕ dq Electrical ϕdq N m f dl Extension f dl Nm-1 m2 γ dσ Surface expansion γdσ Pa m3 pex dV Expansion -pexdV Type of w dw Comments Units Varieties of work 2.3 Expansion work
版权所有：华东理工大学物理化学教研室 18 In general, the work done on a system can be expressed in the form dw = -Fdz, where F is a 'generalized force and dz is a 'generalized displacement'. V C ϕ dq Electrical ϕdq N m f dl Extension f dl Nm-1 m2 γ dσ Surface expansion γdσ Pa m3 pex dV Expansion -pexdV Type of w dw Comments Units Varieties of work 2.3 Expansion work
版权所有：华东理工大学物理化学教研室 19 No work is done when a system expands freely. Expansion of this kind occurs when a system expands into a vacuum. 2). Free expansion pex = 0 dw = 0 for each stage of the expansion w = 0 Free expansion: the expansion against zero opposing force. 2.3 Expansion work
版权所有：华东理工大学物理化学教研室 19 No work is done when a system expands freely. Expansion of this kind occurs when a system expands into a vacuum. 2). Free expansion pex = 0 dw = 0 for each stage of the expansion w = 0 Free expansion: the expansion against zero opposing force. 2.3 Expansion work
版权所有：华东理工大学物理化学教研室 20 The magnitude of w, is equal to the area beneath the horizontal line at p = pex lying between the initial and final volumes. = − ∫ fi d ex VV w p V 3). Expansion against constant pressure = − pex (Vf −Vi) = − pexΔV For an expansion of the external pressure constant throughout of the expansion 2.3 Expansion work
版权所有：华东理工大学物理化学教研室 20 The magnitude of w, is equal to the area beneath the horizontal line at p = pex lying between the initial and final volumes. = − ∫ fi d ex VV w p V 3). Expansion against constant pressure = − pex (Vf −Vi) = − pexΔV For an expansion of the external pressure constant throughout of the expansion 2.3 Expansion work