<Li> the solvent has an activity of unity (only a valid approximation for rather dilute solutions) </Li> <Li> At a low concentration, the activity of a solute can be approximated to the ratio of its concentration over the standard concentration: </Li> <Dl> <Dd> <Dl> <Dd> <Dl> <Dd> a i = c i c ⊖ (\ displaystyle a_ (i) = (\ frac (c_ (i)) (c ^ (\ ominus)))) </Dd> </Dl> </Dd> </Dl> </Dd> </Dl> <Dd> <Dl> <Dd> <Dl> <Dd> a i = c i c ⊖ (\ displaystyle a_ (i) = (\ frac (c_ (i)) (c ^ (\ ominus)))) </Dd> </Dl> </Dd> </Dl> </Dd>

Why is the activity of a solid 1