There are two types of liquid solutions : (I) Ideal solution and (II) Non-ideal solution.I. Ideal solution : A solution which obeys Raoult’s law of vapour pressure is called an ideal solution. In these solutions, intermolecular forces between A-A and B-B molecules are same as thatof between A and B. $\Delta H_{\mathrm{mixing}} = 0 ; \Delta V_{\mathrm{mixing}} = 0$ Examples : (i) Benzene + toluene (ii) n-Hexane + n-heptane (iii) Chlorobenzene + bromobenzene (iv) Ethyl bromide + ethyl iodide II. Non-ideal solution : Asolution which does not obey Raoult’s law of vapour pressure is called non-ideal solution. They are of two types. (a) Non-ideal solution with negative deviation: When intermolecular forces between A and B are stronger than between A-A and B-B, then intermolecular force increases, volume decreases, vapour pressuredecreases and heat is released. Hence, $\Delta V = - \mathrm{ve}, \Delta H = - \mathrm{ve}, \Delta P = - \mathrm{ve}$ This is why, the solution is known as non-ideal solution with –ve deviation. $P_A < x_A P^{0}_A, P_B < x_B P^{0}_B$ and $P_S < x_A P^{0}_A + x_B P^{0}_B$ Examples : (i) Chloroform + acetone (ii) Water + sulphuric acid (iii) HCl + water (iv) Acetone + aniline (b) Non-ideal solution with positive deviation:When intermolecular forces between A and B are weaker than that of A-A and B-B. In this case intermolecular force decreases, volume increases, vapour pressure increases, enthalpy increases. $\Delta V = + \mathrm{ve}, \Delta H = + \mathrm{ve}, \Delta P = + \mathrm{ve}$ So, it is called non-ideal solution with positive deviation. $P_A > x_A P^{0}_A, P_B > x_B P^{0}_B$ and $P_S > x_A P^{0}_A + x_B P^{0}_B$ Examples : (i) Ethanol + water (ii) Chloroform + ethanol