Combination Reaction

Chemistry
Concept:- Combination Reaction

A reaction in which two or more reactants, combine to form a single product, is called Combination Reaction.

Example:

Calcium oxide reacts vigorously with water to produce slaked lime
(calcium hydroxide) releasing a large amount of heat.
CaO(s) + H2O(l) → Ca(OH)2(aq)




A solution of slaked lime produced by the reaction is used for white washing
walls. Calcium hydroxide reacts slowly with the carbon dioxide in air to form a thin
layer of calcium carbonate on the walls. Calcium carbonate is formed after two to
three days of white washing and gives a shiny finish to the walls. It is interesting to
note that the chemical formula for marble is also CaCO3.

Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)



The heat evolved in the above reaction is very large. Reactions in which heat is
released along with the formation of products are called exothermic
chemical reactions.
Other examples of exothermic reactions are –
(i) Burning of natural gas
CH4(g) + 2O2 (g) → CO2 (g) + 2H2O (g)


Respiration is an Exothermic Process

Respiration involves the breakdown of complex food into simple forms. During digestion,the food we eat is broken down into simpler
substances. For example, rice, potatoes and bread contain
carbohydrates. These carbohydrates are broken down to form glucose.
This glucose combines with oxygen in the cells of our body and provides
energy. The energy is released in the from of heat. hence, respiration is also an exothermic reaction.