Activity of a component in any solution Raoults and Henry s laws

Activity of a component in any solution Raoult s and Henry s laws 

Let us consider component i in a solution whose molar fraction x varies between 0 and 1 at a given temperature and pressure. In the pure compound reference, the activity of this compound will be given by  

If we make x tend towards 1, we know that tends towards 1. According to expression [3.20], a solution, for which the coefficient of activity (convention (I)) equals 1, is an ideal solution. Therefore, when the molar fraction of a component tends towards 1, the behavior of this component tends towards that of an ideal solution this is what we call Raoult s law. 

Now let us examine the behavior of the same activity of i when the molar fraction of i tends towards zero. The solution then behaves with regard to i as an ideal dilute solution. Such a solution is defined by a coefficient in reference (II) which equals 1. Its coefficient of activity in reference (I) will therefore be given by relation [3.33] the activity of / in convention (I) in an infinitely dilute ideal solution is  

A tendency of molecules in components 1 and 2 to attract leads to solutions with a negative deviation with regard to Raoult s law 1) whereas the tendency of molecules to repel leads to solutions with a positive deviation with regard to Raoult s law 1). 

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