Question

Define the terms: Boiling point.

Answer 1

Hint: The temperature at which conversion of liquid on heating takes place at standard atmospheric pressure is called the boiling point of that liquid and the phenomenon is called boiling.

Complete step by step solution:
-Atmospheric pressure is sometimes called the barometric pressure. On the Earth, the atmospheric pressure (at sea level) is defined as 1 atmosphere (atm). Pure water at standard pressure (1atm) boils at $100{}^\circ C$.
-Water reaches the standard atmospheric pressure \[100{}^\circ C\]. This measurement is taken at the sea level, where the full weight of the earth’s atmosphere presses down upon the water. As the elevation rises, water can boil at a lower temperature. At the peak of Mount Everest, water boils at nearly \[72{}^\circ C\].
-At the boiling point, the temperature no longer rises with the heat added because the energy is only again being used to break all the intermolecular bonds. Once all water has been boiled to its steam, the temperature will continue to accent linearly as heat is added.
-The boiling point of a liquid usually depends on the following factors:
(i) Atmospheric Pressure
(ii) Impurities present
(iii) Intermolecular forces
-The biggest factor in the determination of a liquid’s boiling point is its surrounding pressure.
-Higher melting and boiling points signify stronger non-covalent intermolecular forces. Consider the boiling points of increasingly larger sized hydrocarbons. Greater the number of carbons means a greater surface area possible for hydrophobic interaction, and thus higher boiling points.
-The boiling point of a substance generally depends on its intermolecular forces of interaction such as van der Waal forces, dipole-dipole, ion-dipole, H-bonding, etc. The higher the strength of the magnitude of attraction among molecules more will be the boiling point.
-Ethyl alcohol has its boiling point \[78.5{}^\circ C\]at sea level. It is a liquid at room temperature and the bonds between its molecules are comparatively strong. On its contrast, methyl ether has a boiling point of \[-25{}^\circ C\]. At room temperature and sea level, methyl ether is a gas.
-The effect of impurities on the boiling point of a liquid is it increases the boiling point due to a process called boiling point elevation.
-The boiling point is also a colligative property. Adding impurities in liquids increases the boiling point as due to the presence of impurities decreases the number of water molecules that are available to vaporize, thus the vapour pressure of the solution becomes lower than the pure solvent. As a result, the solution has to be heated much more to make vapour pressure equal to atmospheric pressure and thus the compound boils at a higher temperature.

Note: The simplest way to alter the boiling point of a liquid is to change its surrounding pressure. Using a closed system to manually enhance that pressure will raise the boiling point of that liquid. Lowering the surrounding pressure, either by increasing altitude or by creating a vacuum, will decrease the same liquid’s boiling point. The boiling point of a liquid is dependent upon the strength of the bonds between its molecules. Thus, adding a solute to the liquid will create stronger bonds between molecules, increasing the solution’s boiling point without increasing pressure.