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From Wikipedia, the miễn phí encyclopedia

A direct combination reaction (also known as a synthesis reaction[1]) is a reaction where two or more elements or compounds (reactants) combine đồ sộ size a single compound (product). Such reactions are represented by equations of the following form: X + Y → XY (A+B → AB). The combination of two or more elements đồ sộ size one compound is called a combination reaction. In other words, when two or more elements or compounds react sánh as đồ sộ size one single compound, then the chemical reaction that takes place is called a combination reaction. | a)- Between elements | C + O2 → CO2 | Carbon completely burnt in oxygen yields carbon dioxide |- | b) Between compounds | CaO + H2O → Ca(OH)2 | Calcium oxide (lime) combined with water gives calcium hydroxide (slaked lime) |- | c) Between elements and compounds | 2CO + O2 → 2CO2 | Oxygen combines with carbon monoxide,And carbon dioxide is formed. |}

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There is no specific number of reactants in a combination reaction.

Combination reactions are usually exothermic because when the bond forms between the reactants, heat is released. For example, barium metal and fluorine gas will combine in a highly exothermic reaction đồ sộ size the salt barium fluoride:

                              Ba + F2BaF2

Another example is magnesium oxide combining with carbon dioxide đồ sộ produce magnesium carbonate.

                              MgO + CO2MgCO3

Another example is iron combining with sulfur đồ sộ produce iron(II) sulfide.

                              Fe + SFeS

When a combination reaction occurs between a metal and a non-metal the product is an ionic solid. An example could be lithium reacting with sulfur đồ sộ give lithium sulfide. When magnesium burns in air, the atoms of the metal combine with the gas oxygen đồ sộ produce magnesium oxide. This specific combination reaction produces the bright flame generated by flares.

Combination reactions can also occur in other situations when the two products bởi not have the same ionic charge. In such a situation, different quantities of each reactant must be used. To denote this in a chemical equation, a coefficient is added đồ sộ one or more of the reactants sánh that the total ionic charge of each reactant is the same. For example, Iron (III) Oxide is formed by the following equation: . This is because in this case, Iron has a charge of 3+ while each Oxygen atom in has a charge of 2-. Oxygen Gas () must be used instead of elemental oxygen () because elemental oxygen is a miễn phí radical that is unstable and combines with other oxygen atoms đồ sộ size .

Another example natural conditions. Likewise, the Hydrogen atoms should be in the size because is an unstable miễn phí radical not commonly found in nature; the chemical equation is also generally impossible under natural conditions. There are some types of combination reactions

(a) Combination reactions between two elements.

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(b) Combination reactions between two compounds.

(c) Combination reactions between an element and a compound.

In all the above reactions, one single compound is formed. For example,

(i) Combination Reaction Between two Elements

a) Hydrogen reacts with oxygen đồ sộ size water i.e Combustion of Hydrogen forms Water (do note that this reaction is an exothermic one).

     + heat

b) Hydrogen reacts with chlorine đồ sộ size Hydrogen chloride(also known as hydrochloric acid)


(ii) Combination Reaction Between two Compound

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a) Calcium oxide (quick lime) reacts with water đồ sộ size calcium hydroxide (stalked lime)


Here is another example of synthesis reaction or direct combination reaction , in this there are three reactants and they size a single product .

  • Nitrogen reacts with water and oxygen đồ sộ size ammonium nitrate .