... βU , (1 .85 )andtheoneinEq.(1 .84 )asσ =logZgc+ βU + ηN . (1 .86 )Using Eq. (1. 58) one can expressed the Lagrange multipliers β and η asβ =µ∂σ∂U¶N, (1 .87 )η =µ∂σ∂N¶U. (1 .88 )The chemica ... systems denoted as S1 and S2.Letσ1= σ1(U1,N1 )and σ2= σ2(U2,N2)betheentropyofthefirst and second system respectivelyEyal Buks Thermodynamics and Statistical Physics 19Chapter 1. ... =τkB. (1.92)When the grandcanonical partition function is expressed in terms of β and µ (instead of in terms of β and η), it is convenient to rewrite Eqs. ( 1 .80 ) and (1 .81 ) as (see homework exercises...