Question 7
Give reasons:
(a) A gas can fill the whole vessel in which it is enclosed.
(b) Solids cannot be compressed.
(c) Liquids can flow.
(d) When magnesium is burnt in air, there is an increase in mass after the reaction.
(a) The particles of gases lie far apart from each other and the intermolecular spaces are therefore very large. The intermolecular forces of attraction are so weak that the particles are free to move and they have high kinetic energy, so they fill the whole vessel in which it is enclosed.
(b) In solids, the particles are closely packed. There is a strong force of attraction between the particles and the intermolecular space is almost negligible. The molecules are therefore not free to move. They only vibrate about their mean positions. This makes solids difficult to compress.
(c) In liquids the molecules are loosely packed and the intermolecular forces of attraction is not so strong as solids. The intermolecular space is larger and kinetic energy is more as compared to solids. The particles can move freely and randomly which makes the liquids to flow.
(d) When magnesium is burnt in air, it forms magnesium oxide. The mass of magnesium oxide is found to be more than the mass of magnesium because the mass of oxygen used is not taken into consideration. If that is considered the total mass of the reactants and the products are found to be almost equal.
2Mg + O2 2MgO