When a strong acid, strong base or their salt are dissolved in water, they are completely ionised. If a strong acid is added to a strong base, ions from the former combine with ions of the latter forming water. The formation of each water molecule liberates a certain quantity of energy and the reaction is exothermic. The heat liberated when one mole of water is formed by combining hydrochloric acid and sodium hydroxide is 13.7 kcal . The heat liberated when one mole of water is formed by combining sulphuric acid and sodium hydroxide is