Check for slaking of lime using your favorite search engine . The formation of slaked lime (calcium hydroxide, Ca(OH)2) when water is added to lime (CaO) is exothermic. It is heated because it releases energy in the form of heat, because the new substance formed (slaked lime) has less internal energy than the original and this is released in the form of heat. It is an exothermic chemical reaction. 2Ca + O2 -> 2CaO -> burning calcium creates heat so it is exothermic so the decomposition of CaO is therefore endothermic i.e. This method is called the slaking of lime. 2. Adding Water to Quick Lime In the preparation of whitewash, the addition of water to quick lime results in temperature gain. Breizh . 2) Most neutralisation reactions are exothermic. Back to top #2 breizh breizh. Why is heat produced when we add water (H2O) to calcium oxide (CaO)? We say, for example, “chemically combined together”. Be sure to understand what the question is actually asking though. CaO can be decomposed - e.g. As a general rule, acid and base solutions are exothermic. You should not have used the word “combine” in your question. In the output mode, an exothermic reaction is initiated when liquid water or steam is injected into the metal oxide particle bed to produce Ca(OH)2 or Mg(OH)2. When water is mixed with lime (calcium oxide), water is absorbed and a lot of heat is generated. Some examples are listed below. Calcium oxide reacts violently with water, causing it to reach 90 C. It then forms calcium hydroxide, also called slaked lime. Gold Member. Forum Moderator 4,780 posts Posted 30 December 2019 - 07:12 PM. 1) The combustion of methane (natural gas) is highly exothermic (it gives out a lot of heat). Examples and Uses of Endothermic and Exothermic Reactions. 3) Adding concentrated sulfuric acid to water is highly exothermic. by electrolysis - alternatively reduction via other compounds. Most chemical reactions are exothermic. Formation of water from molecular hydrogen and oxygen and the formation of a metal oxide such as calcium oxide (CaO) from calcium metal and oxygen gas are examples. Reaction of Zinc and Hydrochloric Acid CaO(s) + H2O(l) Ì¢ ÛÊ Ûª Ca(OH)2(aq) + Heat. The correct word is “mix”. requires energy. This exothermic reaction can represented as the following equation: Calcium Oxide + Water Ì¢ ÛÊ Ûª Calcium hydroxide + Heat. The basic operating principle involved in the TES system is a thermochemical reaction involving metal oxides such the calcium oxide (CaO) or magnesium oxide (MgO) and water. As a result, calcium hydroxide (Ca(OH)₂) and heat are generated. Both ways involve putting energy in. CaO + H₂O = Ca(OH)₂ + Heat (15,500 kcal) Calcium oxide water calcium hydroxide. Hi, From literature : CaO (s) + H2O (l) --- > Ca (OH) 2 (aq) (∆Hr = −63.7 kJ/mol of CaO) exothermic reaction. In chemistry the word “combine” has a special meaning.