CONCEPTS BOOSTER

Question: An aqueous solution is 1.00 molal in KI. Which change will cause the vapour pressure of the solution to increase? 1. Addition of NaCl 2. Addition of Na2SO4 3. Addition of 1.00 molal KI 4. Addition of water Answer:  An aqueous solution is molal in . So, the addition of water will cause the vapour pressure to increase. This is according to Raoult's Law. In the other three options, electrolyte undergo ionization, which leads to lowering of vapour pressure. Hence, the correct option is D Or  According to raoults law Ps = PoXa (Xa = mole fraction of solvent) and on addition of water the mole fraction of water in the solution increases therefore vapour pressure increases.

NOTES ON THERMAL PROPERTIES OF MATTER Heat:- Heat is the agent which produces in us the sensation of warmth and makes bodies hot. It is form of energy. The part of thermal energy which flows from one body to the other due to temperature difference is called heat. Nature of heat:- (a) The weight of a body remains the same weather it is heated or cooled. (b) Heat flows from higher to lower temperature (c) In any exchange of heat, heat lost by the hot body is equal to the heat gained by the cold body. (d) Substances generally expand when heated (e) A certain amount of heat known as latent heat is required to change the state of a body from solid to liquid or from liquid to gas without any change in temperature. Thermal Energy:- In accordance to dynamical theory of heat the sum total of translational, vibrational and rotational energies of the molecules of a system is called the thermal energy of the system . Unit of Heat:- (a) Calorie (cal):- It is the amount of heat required ...