Physical Chemistry Nonideal Solutions Activity and Activity Coefficients The activity a; is more convenient to use in numerical calculations than ur (a)we can not determine absolute value of u; (more relative values) (b)A→>-0,asx->0. ca can be compared withxcar nd y with 1)to judge the degree of nonideal a.→)x.aSx.→1 y→>1,asx1>111 Activity and Activity Coefficients Nonideal Solutions (c) ai can be compared with xi (and i with 1) to judge the degree of nonideality. (a) we can not determine absolute value of i (more relative values). The activity ai is more convenient to use in numerical calculations than i . → −, → 0. i i (b)  as x → , →1. i i i a x as x →1, →1. i i  as x Physical Chemistry