Decomposition Reaction

Decomposition Reaction It's Process and Chemical Reaction

Chemical Reactions:

The process by which chemicals work together to form new chemical by means of different compositions are called as chemical reactions and also where the reactants are transformed into products. The ways in which an element or compound undergoes changes in composition is stated by the chemical properties of the element or compound.

Usually, a chemical reaction will be represented by a chemical equation which will represent the change from reactants to products. In a chemical equation, the left-hand side will represent the reactants and the right-hand side will represent the products of the reaction. In order to show the relative amounts of reactants and products involved in the reaction, a chemical reaction will be written with stoichiometric coefficients.

In a chemical reaction, a parenthetical note of the compound’s state will be given for each compound i.e. for solid as (s), for liquid as (l) and for gas as (g) and for an aqueous solution in which the compounds are dissolved in water, the symbol (aq) will be used.

A form of a chemical reaction will be like:

A (aq) + B(g) → C(s) + D(aq)

Here, A and B react together to form the products C and D.

In order to provide an exact chemical equation, the following things must be present:

  • • Every reactants and product must be written using their chemical formulas. For example H₂

  • • Each element’s number of atoms must be equal on both sides of the equation. In order to balance the number of atoms, their coefficients will be used in front of the chemical formulas. Example: 2Mg + O₂ → 2MgO

  • Types of chemical reactions:

    Precipitation or double replacement reaction:

    Precipitation is a reaction that occurs when aqueous solutions of cations which are positively charged ions and anions which are negatively charged ions. A precipitate is the insoluble solid and the remaining liquid is the supernate.

    Acid-base or neutralization reaction:

    A reaction which occurs on mixing an acid and base together is called a neutralization reaction. H+ ions are produced by an acid substance and OH- ions are produced by a base substance.

    Salt and water which is an ionic compound will be produced by an acid-base reaction. The reaction between hydrochloric acid and sodium hydroxide is an example of a typical acid-base reaction.

    Following is the equation for the above-mentioned reaction:

    HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)

    In the reaction mentioned above, HCl and NaOH are the acid and base substances and the salt is NaCl.

    Oxidation-reduction or redox reactions:

    When the oxidation number of the atoms involved in a reaction is changed, the redox reaction occurs. The process by which an atom’s oxidation number is increased is called the oxidation process. The process by which an atom's oxidation number is decreasing is called a reduction reaction.

    A reaction between hydrogen gas and fluorine gas is the example of a redox reaction.

    H₂ (g) + F₂ (g) → 2HF(g)

    In the above-mentioned reaction, the hydrogen is oxidized from 0 to +1 oxidation state and so this is the reducing agent. As it is reduced from 0 to -1, fluorine is the oxidizing agent.

    Combustion reaction:

    A type of redox reaction during which a fuel reacts with an oxidizing agent, resulting in the release of energy as heat is called a combustion reaction. Such reactions where the energy is given off are called exothermic reactions and the reactions which absorb heat are called endothermic reactions.

    Following is the example for a combustion reaction of glucose.

    C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

    Synthesis reactions:

    When one or more compounds combine together to form a complex compound, a synthesis reaction is said to occur.

    Silver combines with oxygen gas to form silver oxide is an example of a synthesis reaction.

    2Ag + O₂ → 2AgO

    Decomposition reaction:

    The opposite of synthesis reaction is called as the decomposition reaction. In the process of decomposition reaction, many complex compounds break down into multiple simpler compounds.

    The separation of a substance or material into two or more substances or materials that might differ from each other and from the original or unique substance are called as the decomposition reaction.

    From our day to day life to a chemical lab, the decomposition reaction takes place everywhere. The digestion process is a type of decomposition reaction where the food is broken down in order to form water, carbon dioxide, and heat, so it is an important type of reaction.

    The common example of the decomposition reaction is the digestion of food in our body. Here the food like proteins, fats, carbohydrates etc will decompose into a number of simpler and smaller units. In order to keep our body working, a further reaction takes place to release a large amount of energy.

    The decomposition of hydrogen peroxide into oxygen and hydrogen gas is a typical example of the decomposition reaction.

    H₂ O₂ → H₂ + O₂

    Classification of decomposition reaction:

    Thermal composition reaction or thermolysis is the decomposition by means of heat. Electrolytic decomposition reaction or electrolysis is the decomposition by means of electricity. Photodecomposition reaction or photolysis is the decomposition by means of light.

    Decomposition reaction can be classified into three types. They are as follows:

    1. Thermal decomposition reaction:

    A chemical reaction where a single substance breaks into two or more simple substances when heated is called a thermal decomposition reaction. Since the heat is required to break the bonds present in the substance, this reaction is usually endothermic.

    Calcium carbonate decomposition reaction:

    Limestone or calcium decomposes into quick lime or calcium oxide and carbon dioxide when heated. The major constituent for cement is quick lime.

    Potassium chlorate decomposition reaction:

    Potassium chlorate decomposes into potassium chloride and oxygen when heated strongly and this reaction is used for oxygen preparation.

    In the presence of manganese dioxide, if decomposition is carried out then it will take place at a lower temperature. Manganese dioxide is used as a catalyst in this reaction.

    Lead nitrate decomposition reaction:

    When a little quantity of powdered colourless lead nitrate is taken in a dry test tube and heated over a burner then it can be observed that brown fumes of nitrogen dioxide will evolve out and a yellow residue of lead oxide will be left behind in the tube. When a burning candle is put on the mouth of a test tube, it will catch fire and start to burn again. The oxygen gas is also evolved during this reaction as shown here.

    Hydrated oxalic acid decomposition reaction:

    The decomposition of hydrated oxalic acid into oxalic acid and water is obtained when heated.

    2. Electrolytic decomposition reaction:

    When an electric current is passed through an aqueous solution of a compound, it may result in an electrolytic decomposition reaction. Electrolysis of water is a good example of the electrolytic decomposition reaction.

    Electrolysis of water: The decomposition of water into oxygen and hydrogen due to the passage of electric current through it is called as the electrolysis of water.

    Sodium chloride decomposition reaction:

    When electricity is passed through molten sodium chloride, it gets decomposed into sodium and chlorine.

    3. Photodecomposition reaction or photolysis:

    Silver chloride decomposition reaction:

    When a small amount of silver chloride (AgCl) is taken in a watch glass which is kept in sunlight for sometimes, then slowly the crystals acquire a grey color. The decomposition of silver chloride into silver and chlorine is caused by the sunlight as per the analysis.

    The same way, silver bromide to gets decomposed.

    Hydrogen peroxide decomposition reaction:

    The decomposition of hydrogen peroxide into water and oxygen happens in the presence of light.

    Either from light, heat or electricity, most of the decomposition reactions require energy. The breaking of the bonds present in the reacting substance which decomposes to give the product is caused due to the absorption of energy.

    Examples of decomposition reactions:

    When carbonates get heated, it gets decomposed into metal oxides and carbon dioxide.

    CaCO3 (s) → CaO (s) + CO2 (g)
    Na2CO(s) →Na2O (s) + CO2 (g)

    Decomposition of oxy acids results in the formation of carbon dioxide and water.

    H2CO3 → H2O (l) + CO2 (g) 

    Double decomposition reaction:

    A reaction between two compounds in which parts of each compound is interchanged in order to form two new compounds is called a double decomposition reaction. A reaction between two compounds where the positive ion of one compound is exchanged with another compound's positive ion is called a double replacement reaction.

    Uses of decomposition reaction:

    For the extraction of metals, the decomposition reactions are used in the following ways:
    Using electrolytic decomposition, metals are extracted from their molten salts.

    Example: from the naturally occurring ore of zinc, zinc carbonate is first decomposed to give zinc oxide and then reduced to obtain zinc metal.