Question

 

1. Understand the process of vaporization and how it changes with temperature, surface area, and the degree of intermolecular forces.

2. Understand that molecules or atoms have a distribution of thermal energies that changes as a function of temperature.

3.Know that the heat of vaporization, DH_vap, is a quantitative measure for the process of vaporization.

4. Calculate and interconvert mass, moles, and energy using the heat of vaporization.

5 Know and understand how vapor pressure and dynamic equilibrium dictate vaporization and condensation.

6 Know that the vapor pressure of a liquid depends on temperature and that the boiling point of a liquid depends on the external pressure.

7 Use the Clausius-Clapeyron equation to relate temperature and vapor pressure.

8. Define critical temperature and critical pressure.

 

Answer 1

1. Vapourization is the process of conversion of a substance from liquid to vapour phase. The transformation takes place when the molecules acquire enough energy to overcome the intermolecular forces of attraction.
Vapourization at the temperature at which the vapour pressure of the substance becomes equal to the atmospheric pressure is called boiling. This is a bulk phenomenon.
The boiling temperature is an indication of the strength of the intermolecular forces. Stronger the inter molecular attractions, higher the boiling point.
Vapourization at any temperature below the boiling point is called evaporation. This is a surface phenomenon. The rate of evaporation increases with the increase in surface area and temperature of the surroundings.
2.
Thermal energy of a particle(molecule or atom) = 1/2k_BT
T is the absolute temperature.
k_B is is the Boltzmann constant.
k_B = 1.38 x 10^-23 J/K
3.
The quantity of heat energy required to convert one mole of substance from liquid to vapour state at its boiling point is called the enthalpy of vapourization.
5. On heating a substance to its boiling point in a closed container establishes a state of dynamic equilibrium.
For example: Heating water to 100°C in a closed container.

Vapourization and condensation are reversible processes.
At equilibrium, the rate of vapourization is equal to the rate of condensation. The total pressure of the system at this temperature is equal to the atmospheric pressure.
6. Vapour pressure of a liquid is directly proportional to the temperature.
The substance begins to boil when the vapour pressure is equal to the external pressure.
7.
In a vapour - liquid system, the ratio of the vapor and liquid concentrations becomes constant at equilibrium and this equilibrium constant is a function of temperature.  The saturation pressure of the water vapor increases with temperature. The rate of increase in vapor pressure per unit increase in temperature is given by the Clausius-Clapeyron equation.

L is the latent heat of vapourization.
P is the saturation vapour pressure.
T temperature on the absolute scale.
V_v is the specific volume of the vapour.
V_l is the specific volume of the liquid.
8.
Every gas has to be cooled to a minimum temperature before it can be liquefied. This is important so that kinetic energy of the molecules is significantly lowered so that the intermolecular forces take over to convert the substance from vapour to liquid state. This temperature is unique and specific for each gas and is referred  to as the critical temperature.
At the critical temperature the gas will liquefy on application of a minimum pressure, which is the critical pressure of the gas.