Define each of the following reactions??

A.single-replacement reaction


B.direct combination reaction


C.double-replacement reaction


D.decomposition reaction

Define each of the following reactions??
A.single-replacement reaction





During single replacement, one element replaces another element in a compound. There are two different possibilities:





1. One cation replaces another. Written using generic symbols, it is:





AX + Y ---%26gt; YX + A





Element Y has replaced A (in the compound AX) to form a new compound YX and the free element A. Remember that A and Y are both cations (postively-charged ions) in this example.





Some examples are:





Cu + AgNO3 ---%26gt; Ag + Cu(NO3)2


Fe + Cu(NO3)2 ---%26gt; Fe(NO3)2 + Cu


Ca + H2O ---%26gt; Ca(OH)2 + H2


Zn + HCl ---%26gt; ZnCl2 + H2





Notice how, when hydrogen gets displaced, it is written as a diatomic. This is because elemental hydrogen is diatomic.


2. One anion replaces another. Written using generic symbols, it is:





A + XY ---%26gt; XA + Y





Element A has replaced Y (in the compound XY) to form a new compound XA and the free element Y. Remember that A and Y are both anions (negatively-charged ions) in this example.





e.g.





Cl2 + NaBr ---%26gt; NaCl + Br2


Br2 + KI ---%26gt; KBr + I2


In single replacement, one reactant is always an element. It does not matter if the element is written first or second on the reactant side. The other reactant will be a compound.








B.direct combination reaction





A Combination Reaction or a Synthesis Reaction is a general category of a chemical reaction (the term usually refers to an inorganic chemical reaction), in which two or more reagents are chemically bonded together to produce a single product.





For example, the addition of sulphur and iron to form iron sulphide is a combination reaction.





A combination reaction can be of three types:


a) Between 2 elements


b) Between 2 compounds


c) Between an element and a compound





Examples:


a) 2Mg+O2 → 2Mg0


b) O+H2O → H2O2


c) 2C(s) +O2(g) → 2CO2 (g)








C.double-replacement reaction





During double replacement, the cations and anions of two different compounds switch places.





Written using generic symbols, it is:





AB + XY ---%26gt; AY + XB





A and X are the cations (postively-charged ions) in this example, with B and Y being the anions (negatively-charged ions).





Here is another way to look at the above generic example:





a) the outside portions (the cation A and anion Y) combine to make a formula called AY.


b) The inside portions (the anion B and the cation X) switch order so that X (postively charged) goes first and B (negatively charged) goes second making a formula called XB.


Keep in mind that, when it comes to writing actual formulas, you MUST write chemically correct formulas. Please do not assume from the AY and XB examples that the product formulas will always be one-to-one in terms of positive and negative.





Some examples of actual reactions are:





KOH + H2SO4 ---%26gt; K2SO4 + H2O


FeS + HCl ---%26gt; FeCl2 + H2S


NaCl + H2SO4 ---%26gt; Na2SO4 + HCl


AgNO3 + NaCl ---%26gt; AgCl + NaNO3








D.decomposition reaction





During decomposition, one compound splits apart into two (or more pieces). These pieces can be elements or simpler compounds





Written using generic symbols, it is usually shown as:





AB ---%26gt; A + B





However, that really only works for splitting apart into the elements, like these examples.





HgO ---%26gt; Hg + O2


H2O ---%26gt; H2 + O2


MgCl2 ---%26gt; Mg + Cl2


FeS ---%26gt; Fe + S





Decomposition can also split one compound into two simpler compounds (or compound and an element) as in these examples:





CaCO3 ---%26gt; CaO + CO2


Na2CO3 ---%26gt; Na2O + CO2


KClO3 ---%26gt; KCl + O2


Ba(ClO3)2 ---%26gt; BaCl2 + O2


Notice how, in every case so far, there is only one substance on the left-hand (reactant) side. This is always the case in a decomposition reaction.





Figuring out what the products are in decomposition is harder because you will have to recognize several categories of decomposition reactions. Here are your first three:





1) All binary compounds (like the four in the first example set above) will break down into their elements.


2) All carbonates (like the first two in the second example set above) break down to the oxide and carbon dioxide.


3. Chlorates (like KClO3 and Ba(ClO3)2 in the example) will break down to the binary salt and oxygen.








hope this helps:-)