[Big-Daddy]

If the concentration of A in sample 1 of volume V₁ is c_A,1, and the concentration of A in sample 2 of volume V₂ is c_A,2, the concentration of A when sample 1 is mixed with sample 2 is simply Σ(n_A)/Σ(V)=Σ(c_A,section*V_section)/Σ(V).

What do we do for activity? Can we write something similar, or is it not possible to combine the activities with no further knowledge than this.

[AWK]

We should calculate a new activity (activity coefficient) for a final concentration of A using the appropriate aproximation depending on concentration.

[Big-Daddy]

Uh huh so as I thought it isn't additive. We can't do the problem without knowing about the specific species or concentrations involved.

Thanks for the reply, I won't worry too much more about this. It was only a matter of curiosity and I had already supposed that it wouldn't be as simple as addition.

[Big-Daddy]

One question about this - is it necessary that we know concentration in order to do this (in which case we will calculate the new concentration and then multiply it by the new activity coefficient), or can we calculate the new activity without knowing the concentration, just from knowing the initial activity before volume change?

[AWK]

Usually this is an iterative process

[Big-Daddy]

But can we calculate it, iteratively or not, without the initial concentration? i.e. Given the activity alone, the initial volume, and the new volume, as well as the activity coefficient at the new volume but not the activity coefficient at the initial volume?