What is vapour pressure and What is effect of temperature on vapour pressure ?

VAPOUR PRESSURE:

(1) If a sample of water in its liquid phase is placed in an empty container, some of it will vaporize to form gaseous of water. This change is called evaporation.

(2) The pressure exerted by the vapour (molecules in the vapour phase) over the surface of the liquid at the equilibrium at given temperature is called the vapour pressure of the liquid.

OR

(3) It is the pressure exerted by the vapour when vapours are equilibrium with the liquid.

(4) The pressure exerted by vapours is called unsaturated vapour pressure or partial vapour at non equilibrium condition. 

Factors affecting vapour pressure:

(A) Temperature:.

(1) The temperature at which the vapour pressure of the liquid becomes equal to the atmospheric pressure is called its boiling point.

(2) Vapour pressure is directly proportional to theTemperature so that on increasing temperature the rate of evaporation increases and rate of condensation decreases and hence vapour pressure 

increases.

(3) The dependence of vapour pressure and temperature is given by CLASIUS CLAPERON equation.

(4) Vapour pressure of a particular liquid system is only the function of temperature only. It is independent from all other factors like surface area, amount of liquid, available space etc.

An aqueous solution has 5% urea and 10% glucose by weight. what will be the freezing point of this solution ? ( Kf = 1.86 K Kg per mole)

The vapour pressure of two pure liquids A and B, that form an ideal solution are 100 and 900 torr respectively at temperature T. This liquid solution of A and B is composed of 1 mole of A and 1 mole of B. What will be the pressure, when 1 mole of mixrure has been vaporized?

Acetic acid dimerised to an extent of 30% in benzene . The observed molecular mass (in gm) is...

How much ice will separate if a solution containing 25 g of ethylene glycol [C2H4(OH) 2] in 100g of water is cooled to 10°C? Kf(H2O) = 1.86 (25.05 g)

The dielectric con stant of H2O is 80. The electrostatic force of attraction between Na+ and Cl–will be.

Water is a polar colvent and have dielectric constant 80. As NaCl is a polar compound and like dissolves like so, forces of attraction between Na+ and Cl- ion will reduce to 1/80 in water.

100 g of C6H12O6, (aq.) solution has vapour pressure is equal to 40 torr at certain temperature. Vapour pressre d H20(l) is 40.8 torr at same temperature if this solution is cooled to -0.93°C, what mass of ice wil be seperated out ? ( Kf :1.86 kg mol-1)

Molality of an aqueous solution of glucose (Molar mass :180 gmol-1) is 1.0 m. 590 g of this solution is cooled and the temperature is kept at -30°C. The amount of ice separated out (Kf for water 2 K kgmol-1) is...

The van't Hoff's factor for 0.1 M Ba(NO3)2 solution is 2.74. the degree of dissociation is.

Aqueous solution of 0.004 M Na2SO4 and 0.01 M glucose are iosotonic .The degree of dissociation of Na2SO4 is ..

How can derivatives relation between relative lovering of vapour pressure and molality?

A saturared solution of XCl3 has a vapour pressure 17.20 mm Hg at 20°C, while pure water vapour pressure is 17.25 mm Hg. Solubility product (Ksp) of XCl3 at 20°C is

Calculate the percentage degree of dissociation of an electrolyte XY2 ( normal molar mass=165) in water if the observed molar mass by measuring elevation in boiling point is 65.5.

Which of the following pair of solution (aq.) contain isotonic solution at same temperature? (Assume 100 % ionisation of electrolytes) (1) 0.1 M NaCI and 0.2 M CaCI2(2) 0.1 M NaCI and 0.3 M AICI3 (3) 0.3 M NaCI and 0.1 M AICI3 (4) 0.3 M NaCI and 0.2 CaCI2

Freezing point of pure liquid A is T K. If some amount of non-electrolyte non-volatile impurity is added in A, an ideal solution is formed. On cooling at 200 K, only 30% (by mass) liquid A is present and at 201 K, 60 % (by mass) liquid A is present. The value of T is .

Liquid A and B form ideal solution at temperature T. Mole fraction of A in liquid and vapour phase are 0.4 and 4/13 respectively, when total pressure is 130 torr. The vapour pressure (in torr) of A and B in pure state at temperature T are respectively.

We know that partial pressure of components of a binary solution containing A and B component.

(1) In liquid state:

P_A= P°_A X_A and  P_B= P°_B X_B

(2) In Vapour phase: 

P_A= P_T Y_A  and P_B= P_T Y_B

Where X_A and X_B is mole fraction in liquid state while Y_A and Y_B is mole fraction in vapour phase

What is the relation between Raoult' law and Dalton's ?

According to Raoult's Law: The partial pressure of any volatile component of a solution at any temperature is equal to the vapour pressure of the pure component multiplied by the mole fraction of that component in the solution.

      Where X_A­ and X_B is the mole fraction of the component A and B in liquid phase respectively

According to Dalton's Law:

The vapour behaves like an ideal gas, then according to Dalton's law of partial pressures, the total pressure P_Tis given by:

 Partial pressure of the gas = Total pressure x Mole fraction

                                        P_A = P_T Y_A and P_B =P_T Y_B

Where Y_A­ and Y_B is the mole fraction of the component A and B in gas phase respectively

Combination of Raoult's and Dalton's Law:

(3) Thus, in case of ideal solution the vapour phase is phase is richer with more volatile component i.e., the one having relatively greater vapour pressure

Graph Between 1/Y_A Vs 1/X_A:

According to Dalton's law of partial pressures, the total pressure P_T is given by:

 Partial pressure of the gas = Total pressure x Mole fraction

Where Y_A­ and Y_B is the mole fraction of the component A and B in gas phase respectively

According to Raoult's law:

On rearrangement of this equation we get a straight line equation:

Illustrative Examples:

Liquid A and B form ideal solution at temperature T. Mole fraction of A in liquid and vapour phase are 0.4 and 4/13 respectively, when total pressure is 130 torr. The vapour pressure (in torr) of A and B in pure state at temperature T are respectively.

Solubility of gases and Henry's Law:

2 millimolar solution of sodium ferrocyanide is 60% dissociated at 27°C. osmotic pressure of the slotution is .

Given that 2 millimolar solution of sodium ferrocyanide (Na4[Fe(CAN)6] ) is 60% dissociated at 27°C.

First find van't Hoff facter's (i) than Calculate osmotic pressure (π)= icRT as follow:

Decimolar solution of K4[Fe(CN)6] dissociate by 60% at 27°C. Determine osmotlc pressure in Nature/M2.

We know that osmotlc pressure is equal to the (π) = iCRT then  first Calculate the value of(i) then osmotlc pressure.

A complex is represented as CoCl3.xNH3.Freezing point of its 0.1 molar solution is - 0.558° C (Kf = 18.6) Assuming 100 % dissociation and coordination number of Co(iii) is six , the what is the complex formula ?

We can find the formula of Complex by :