Intermolecular Forces
* Intermolecular forces are attractive and repulsive forces between the interacting atoms and molecules.
* The force of attraction between the two temporary dipoles is known as dispersion force or London force.
* Dipole –Dipole forces are attractive forces that act between the polar molecules with permanent dipole.
* The Dipole –Dipole forces are stronger compared to the other London forces.
* Dipole-Induced Dipole attractive forces operate when a polar molecule with permanent dipole induces a dipole in a non-polar atom or molecule by deforming its electron cloud.
* A special case of Dipole – Dipole interaction called hydrogen bond exists in the molecules with highly polar N-H, O-H or H-F bonds.
* The energy of a body arising from the translational, rotational and vibrational motion of its atoms or molecules is called the thermal energy.
* The balance between the intermolecular forces and the thermal energy of the molecules is responsible for the physical state of matter.
* The physical state of matter depends on the strength of intermolecular bonds and the thermal energy of the particles involved.
* The Government of India and Andhra Pradesh have set up several offices and laboratories in different parts of the state.
Gaseous State: Gas Laws
* Volume, number of moles, pressure and temperature are the four interrelated properties that describe the behavior of gases.
* Boyle’s Law describes the relationship between pressure and volume. It states that volume is inversely proportional to pressure at constant temperature and number of moles.
* Charles’ Law describes the relationship between temperature and volume. It states that volume is directly proportional to temperature at constant pressure and number of moles.
* Avogadro’s Law describes the relationship between volume and number of moles. It states at same temperature and pressure, equal volumes of gases contain equal number of molecules.
Gaseous State: Ideal Gas Equation
* Volume, number of moles, pressure and temperature are the four interrelated properties that describe the behavior of gases.
* Boyle’s Law describes the relationship between pressure and volume. It states that volume is inversely proportional to pressure, at constant temperature and number of moles.
* Charles’ law describes the relationship between temperature and volume. It states that volume is directly proportional to temperature, at constant pressure and number of moles.
* Avogadro’s law describes the relationship between volume and number of moles. It states that at constant pressure and temperature, the volume of a gas is directly proportional to the number of moles of gas.
Gaseous State: Dalton’s Law of Partial Pressure
* The total pressure exerted by a mixture of two or more non-reacting gases is equal to the sum of the partial pressures of individual gases.
* The partial pressure of a gas in a mixture is the product of its mole fraction and total pressure of the mixture of gases.
* Dalton‘s law of partial pressures is useful in calculating the pressure of the dry gas collected over water by downward displacement in the laboratory.
Gaseous State: Kinetic Molecular Theory
* Kinetic Molecular Theory is a set of five assumptions that describes the behaviour of molecules in gas.
* Gases consist of a very large number of extremely small particles called molecules, which are in constant, continuous, random and straight-line motion.
* The molecules of a gas are separated from each other by great distances. Hence the actual volume of all the molecules of the gas is negligible when compared to the total volume occupied by the gas.
* Attractive and repulsive forces between the molecules of a gas are negligible as they are much away from each other.
* Boyle’s Law states that, the volume of a given mass of a gas decreases with increase in pressure at a given temperature.
* Charles’s Law states that at constant pressure, the volume of a given mass of a gas increases with increase in temperature.
* Avogadro’s Law states that equal volumes of all gases under similar conditions of temperature and pressure contain equal number of molecules.
Gaseous State: Behaviour Of Real Gases
* An ideal gas is a gas that obeys the ideal gas equation, pV = nRT, under all conditions of temperature and pressure.
* Real gases do not obey the ideal gas equation at all conditions of temperature and pressure.
* Dutch physicist Johannes Van der Waals gave an explanation for these deviations and modified the ideal gas equation in order to make it applicable to real gases.
* The Van der Waal’s equation is given as (p + \frac{an²}{v²}) (V – nb) = nRT.
* The compressibility factor for ideal gas is 1 as the ideal gas equation is pV = nRT.
* The temperature at which a real gas obeys the ideal gas law over an appreciable range of pressure is known as the Boyle temperature or Boyle point.
Gaseous state: Liquefaction of Gases
* A gas can be converted into a liquid through a process called liquefaction.
* There is a particular temperature beyond which, no matter how much high pressure is applied, a gas cannot be liquefied. This temperature is known as critical temperature.
* The pressure required to liquefy a gas at critical temperature is called critical pressure.
* The volume occupied by one mole of a gas at its critical pressure and at critical temperature is the critical volume (Vc) of the gas.
* The critical temperature of carbon dioxide was found to be 30.98 °C, critical pressure, Pc, to be 73.9 atm and critical volume was found to be 95.6 ml.
* Thomas Andrews observed that all gases on isothermal compression exhibited the same behavior as shown by carbon dioxide.
* A gas can be liquefied below its critical temperature by applying pressure. Therefore, we can say that above the critical temperature, it is a gas but below the critical temperature, it is called vapour.
Gaseous state: Liquid State
* The process by which molecules of a liquid go into the vapour state from the surface of the liquid at any temperature below the boiling point of the liquid is called evaporation.
* Vapour pressure is defined as the pressure exerted by vapour in equilibrium with its liquid at a given temperature.
* The boiling point of a liquid depends upon the external pressure.
* The energy required to increase the surface area of the liquid by one unit is defined as the surface energy.
* The units of surface energy are joule per metre square.
Surface tension may be defined as the force acting per unit length perpendicular to the line drawn on the surface of liquid.
* Sl unit of surface tension is Newton per metre.
* Viscosity is a measure of resistance to flow in liquids, which arises due to the internal friction between its layers as it moves.
* The coefficient of viscosity is defined as the tangential force per unit area required to maintain the unit difference of velocity between two layers unit distance apart.