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