Question

Q9 (ii)
please solve it

Answer 1

Evaporation usually occurs on the surface. Evaporation may occur when the partial pressure of vapor of a substance is less than the equilibrium vapour pressure.Boiling is a phase transition from the liquid phase to gas phase that occurs at or above the boiling temperature.

A gas refers to a substance that has a single defined thermodynamic state at room temperature whereas a vapor refers to a substance that is a mixture of two phases at room temperature, namely gaseous and liquid phase. This also means that a vapor is a substance that has experienced some sort of phase change at room temperature. A gas is a substance whose molecules are in constant free motion past each other and can be compressed, which can also be referred to as a compressible fluid. When no liquid or solid can form at the temperature of the gas it is called a fixed gas.
It is worth noting that when referring to the four states of matter there is a ‘gas phase’ which does not necessarily refer to a gas as a distinct element but rather represents differences in interrelationships of molecules. A gas has its single gas particles vastly separated, making a gas invisible to the eye.

When a substance is at a temperature below its critical temperature it is in a ‘gas phase’ and therefore will be a vapour. A vapour can co-exist with a liquid or solid when they are in equilibrium state. Therefore from this we can infer that a vapour is a gas state of a substance at a temperature where it can co-exist with its liquid or solid state so for a liquid or solid to become vapour it does not have to first boil.

It is also of paramount importance to note that vapour is a result of the two types of vaporization of a liquid which are boiling and evaporation, the transition from liquid phase to ‘gas phase’. Evaporation occurs at the surface of the liquid when its temperature is below the boiling temperature at a given pressure. Boiling occurs below the surface of the liquid.