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, `H^(+)` ions from the former combine with `OH^(-)` 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 sodium hydroxide is 13.7 kcal. The heat liberated when one mole of water is formed by combining sulphuic acid and sodium hydroxide is