A solution is said to be ideal if each of its components obeys Raoult's law for the entire range of concentration (composition). In the preparation of ideal solution, no thermal change is observed. i.e.
△Hmix=0
The force of interaction between A−A, B−B and A−B are of same order. The volume of mixing (△Vmix) is also zero. i.e. The volume of the solution will be equal to sum of the volumes of the two components.
For example, the solution of benzene in CCl4 shows same attractive forces as are present in benzene and CCl4 separately. Another examples are benzene and toluene, bromoethane and chloroethane.
Solutions are non-ideal if they do not obey Raoult's law. i.e.
△Hmix≠0 and △Vmix≠0
Therefore these solution deviate from ideality and depending on type of deviation from ideal behaviour, non-ideal solutions may be classified as showing negative deviation or positive deviation.
