Types of chemical reaction I

One way of classifying chemical reactions are:

• Decomposition reaction
• Combination reaction
• Displacement reaction
• Double Displacement reaction
• Dissociation reaction
• Precipitation Reaction

DECOMPOSITION REACTION:

• A decomposition reaction occurs when a compound is broken into smaller parts. This reaction can be either thermal decomposition or electrolytic decomposition or light decomposition.
• For example, when calcium carbonate is heated, it decomposes to give calcium oxide and carbon dioxide

COMBINATION REACTION OR SYNTHESIS REACTION:

• As the name suggests, in Combination reaction, two or more substances combine to form a new substance or single product.
• For example, Hydrogen burns in oxygen to form water:

DECOMPOSITION REACTION:

• A chemical equation in which the number of atoms of all the molecules is equal on both sides of the equation is known as balanced chemical equation.
• An unbalanced chemical equation has unequal masses of various elements in reactant and product.

• In light decomposition, the compound decomposes due to exposure to light

DISPLACEMENT REACTION OR SUBSTITUTION REACTION:

• In Displacement reaction, an atom or group of atoms in a molecule is replaced by another atom or group of atoms to produce new substances.
• A more reactive element displaces a less reactive element from its aqueous salt solution.

DOUBLE DISPLACEMENT REACTION OR METATHESIS REACTION

• The reaction where two reacting molecules exchange their partner ions in solution is called double displacement reaction.
• This occurs when a strip of zinc metal is placed in copper sulphate solution to produce zinc sulphate solution and copper.
• Likewise, when silver nitrate solution is added to sodium chloride solution, it results in the formation of white precipitate of silver chloride along with sodium nitrate solution:

• Similarly, when an aqueous solution of NaCl is added to an aqueous solution of A_gNO₃, the compounds break down into hydrated Na⁺ and Cl^– ions and Ag⁺ and NO^-3 ions.

• When combined, a double displacement reaction takes place. A soluble compound N_aNO₃ and an insoluble compound A_gCl are formed. This happens when Ag⁺and Cl_– ions combine in the vessel, and a white solid precipitate is formed. As the solid precipitates, the Na₊ and NO_-3 ions remain in solution. Thus, we have the following balanced equation:

NEUTRALIZATION REACTION

• It occurs between an acid and a base forming of salt and water.

• For example,
  ${\mathrm{H}}_2{\mathrm{SO}}_4 + 2\mathrm{NaOH} \to {\mathrm{Na}}_2{\mathrm{SO}}_4 + 2{\mathrm{H}}_2\mathrm{O}$

DISSOCIATION REACTION:

• Dissociation reaction takes place, when a substance breaks up into its ions.
• $$\begin{gathered} •\mathrm{When} \mathrm{Hydrochloric} \mathrm{acid} \mathrm{gas} \mathrm{combines} \mathrm{with} \mathrm{water}, \mathrm{then} \mathrm{it} \mathrm{dissociates} \mathrm{to} {\mathrm{H}}^{+} \mathrm{and} {\mathrm{Cl}}^{–} \left(\mathrm{aq}\right) \\ \mathrm{HCl}\left(\mathrm{g}\right) + {\mathrm{H}}_2\mathrm{O}\left(\mathrm{I}\right) \to {\mathrm{H}}^{+} \left(\mathrm{aq}\right)\left({\mathrm{H}}_3^{+}\mathrm{O}\right) + {\mathrm{Cl}}^{–} \end{gathered}$$

PRECIPITATION REACTIONS:

• Formation of insoluble salts results in the precipitation reaction.
• Although the reactants are soluble, the product formed would be insoluble. It separates out as a solid.
• A precipitation reaction occurs when a solution which originally contains dissolved substances, produces a solid.
• The solid is generally denser and settles at the bottom of the vessel in which the reaction takes place.
• A chemical equation adequately describes reaction in solutions.
• But the typical molecular equation has different representations for reactions of ionic compounds in aqueous solution (water).
• It may indicate formulas of reactants and products that are not present, and eliminate completely the formulas of the ions that are the real reactants and products.
• Ionic equation results if the substance in the molecular equation that are actually present as dissociated ions are written in the form of their ions.
• When lead nitrate reacts with potassium Iodide, a yellow precipitate of lead Iodide and a by-product of potassium nitrate is formed.