At sea-level, external pressure is high and more heat is required to equalize vapour pressure to the external pressure that is why boiling point is high. So the boiling point varies with external pressure. Q.2 viii) A liquid boils at different temperatures at sea-level and at mountains.īoiling point of a substance is the temperature at which vapour pressure of the liquid becomes equal to the external pressure. So it can be distilled easily under vacuum. vacuum, the boiling point of glycerine decreases to 210 oC at 50 mmHg. For example, glycerine boils at 290 oC at normal atmospheric pressure, but it decomposes at this temperature. High boiling sensitive liquids cannot be purified at normal temperature because they decompose before their boiling points are reached. The distillation carried out under reduced pressure is called vacuum distillation. These molecules take energy away from the filled water and water remains cool even in hot summer days. Water molecules come on the surface through these pores and evaporate. Vacuum distillation can be used to avoid decomposition of a sensitive liquid.Įarthenware vessels have porous surface. Stronger the intermolecular forces, slower will be the rate of evaporation and vice versa.įor example, rate of evaporation of water is slower than that of ether, because water has strong hydrogen bonding and ether has weak London forces.ĪDVERTISEMENT Q.2 vii) Earthenware vessels keep water cool even in hot summer days. Q.2 vi) Different liquids have different rates of evaporation even at the same temperature.ĭifferent liquids have different rates of evaporation even at the same temperature because the strength of intermolecular forces is different in different liquids.
Hence neon has less boiling point a as compare to Argon. Due to small size, neon molecules have weaker London dispersion forces while Argon has stronger London dispersion forces due to large size of its molecules. Neon and Argon both are non-polar gases and London dispersion forces which depend upon the size of molecules, are the only forces present in their molecules. Why?īoiling point of a substance is directly related to the strength of attractive forces present among its molecules.
Neon has boiling point of -248☌ while Argon has -189☌. Q.2 v)Neon and Argon both are mono-atomic noble gases of the same group. States of Matter-II Liquids Chemistry Class 11 Notes Chapter 5 17 So water has a higher boiling point due to greater number of hydrogen bonds and a three-dimensional network of hydrogen bonding in its structure. But on average, one molecule of HF forms one hydrogen bond and one molecule of H 2O forms two hydrogen bonds because it has two hydrogen atoms in its molecule. Hydrogen bonds in HF are strong as compared to that of H 2O because of greater electronegativity of fluorine than oxygen. Q.2 iii) H 2O has high boiling point than HF, although Fluorine is more electronegative than oxygen.īoiling point of a substance depends upon the strength of attractive forces present among its molecules. Read more: States of Matter I Gases Chemistry Class 11 Notes States of Matter-II Liquids Chemistry Class 11 Notes Chapter 5 15 Hence HCl is a gas at ordinary temperature. So the dipole-dipole forces among its molecules are not strong enough to keep it in liquid form. On the other hand, due to lower electronegativity of Cl, it cannot undergo hydrogen bonding among its molecules. Strong hydrogen bonding among its molecules makes HF liquid at ordinary temperature. HF has hydrogen bonding among its molecules due to the greater difference of electro-negativities between H and F atoms. Q.2 ii) HF is a liquid at ordinary temperature while HCl is a gas. So the structure of the body would not be stable if the hydrogen bonding is not strong. The hydrogen bonds stabilize these spiral helixes. These chains are coiled around each other and form a spiral helix. Fibres, hair, muscle proteins consist of long chains of amino acids. Large protein molecules in our body are stabilized due to strong hydrogen bonding.
So we will have no liquid water to be used and no survival on earth.