Question

1.  Discuss the process of water boiling from the molecular point of view. Your explanation should include the effect of atmospheric pressure and the effect of adding a non-volatile solute to the water.

2. Compare and contrast Boyle’s Law and Charles’ Law. Make sure to define and explain both laws prior to discussing their similarities and differences.

Answer 1

1. Water has high boiling point in comparison to other monmetallic hydrides due to intermolecular hydrogen bonding. Hence during boiling of water the supplied heat is used in the breaking of intermolecular hydrogen bonding so that the water molecules are separated from each other and evaporate from the surface of water.At a particular temperature each water molecule has a particular value of average kinetic energy. When we supply heat the temperature of water molecules increases and hence kinetic energy. When the temperature becomes 100 DegC, the kinetic energy of water molecules becomes sufficient enough to separate from each other and evaporate making the vapour pressure due to water molecules equal to atmospheric pressure.

The boiling point depends on atmospheric pressure. If the atmospheric pressure is higher than 1 atm, then higher temperature is required to achieve vapor pressure more than 1 atm. Hence boiling point increases with temperature and becomes more than 100 degC. Similarly when the atmospheric pressure is lower than 1 atm, less temperature is required to achieve vapor pressure less than 1 atm.

When a non-volatile solute is added to water, it becomes more diluted and hence the rate of evaporation decreases and hene to achieve the boiling point we need to supply more heat and hence boiling point increases.

2: Boyle's Law: For a closed ideal gas system at constant temperature, the volume of the gas is inversely proportional to pressure i.e PxV = Constant.

Charles Law: For a close system at constant pressure, the volume of the system is directly proportional to temperature. i.e. V/T = constant.

Similarities: Both are applicable only to ideal gases in a closed system.

Both of the laws can be derived from ideal gas equation PV = nRT.

Dissimilarities: In Boyle's law temperature is constant where as in Charle's law pressure is constant.

In Boyles law volume is inversely proportional to pressure at constant temperature, where as in Charle's law volume is directly proportional to kelvin temperature at constant pressure.