Pertains to a @[email protected] of a @[email protected] changing in area at constant mass and is the differential change of its @[email protected] with relative change in area \(A\), \[E=A\ (\frac{\partial \sigma }{\partial A})_{T,p,n_{i}}\] where \(T\) is the @[email protected], \(p\) is the pressure, and \(n_{i}\) is the @[email protected] of the species \(i\).