10th Class Science Chemical Reactions and Equations Types fo Chemical Reactions

       Types of Chemical Reactions

The chemical reactions are of following types

• Combination Reaction
• Decomposition Reaction
• Displacement Reaction
• Double Displacement Reaction
• Precipitation Reaction
• Redox Reaction

           Combination Reaction

Combination reactions are those chemical reaction in which two or more elements or compounds combine together to form a single compound. e.g. Hydrogen and nitrogen reacts to form ammonia

\[3{{H}_{2}}(g)+{{N}_{2}}(g)\to 2N{{H}_{3}}(g)\]

e.g. Burning of carbon

\[{{C}_{(s)}}+{{O}_{2}}(g)\to C{{O}_{2}}(g)\]

For white washing solution of calcium hydroxide (slaked lime is used). It combines with carbon dioxide in air to form a layer of calcium carbonate which gives a shiny appearance to the surface of wall.

             Decomposition Reaction

Those reactions in which single reactant breaks down to give simpler product.

e.g. Ferrous sulphate crystal on heating loses water and decomposes to form ferric oxide , sulphur di oxide and sulphur trioxide.

\[FeS{{O}_{4}}+Heat\to F{{e}_{2}}{{O}_{3}}+S{{O}_{2}}+S{{O}_{3}}\]

             Displacement Reaction

Those reactions in which more reactive element displaces the less reactive element from its salt solution. e.g.

1. If we put iron nail in blue coloured copper sulphate solution, the colour will change to green. It is so because the iron being more reactive than copper and hence displaces it from its salt solution,

 \[Fe(s)+CuS{{O}_{4(aq)}}\to FeS{{O}_{4(aq)}}+Cu\]

    Blue                      Green

1. If chlorine gas is passed through a colourless solution of potassium bromide, the solution turns to yellowish brown. This is because chlorine being more reactive displaces bromine from its salt solution.

\[C{{l}_{2(g)}}+2KB{{r}_{(aq)}}\to 2KC{{l}_{(aq)}}+B{{r}_{2}}\]

The reactivity of metals can be known from the reactivity series of metals which is as follows:

                \[K>Na>Ca>Mg>Al>Zn>Fe>Pb>H>Cu>Hg>Ag>Au\]

              Double Displacement Reaction

Double displacement reaction are those reactions in which two compounds interchange their ions and form two new compounds. e.g.

1. When a solution of silver nitrate is poured into the sodium chloride solution, a white precipitate is formed. This is because of the formation of silver chloride

\[AgN{{O}_{3(aq)}}+NaC{{l}_{(aq)}}\to AgC{{l}_{(s)}}+NaN{{O}_{3(aq)}}\]

1. Similarly when lead nitrate solution is added to potassium iodide, a yellow precipitate of lead iodide is formed.

\[Pb\,{{(N{{O}_{3}})}_{2}}+2Kl\to Pb{{l}_{2(s)}}+2KN{{O}_{3(aq)}}\]

            Precipitation Reaction

Precipitation reactions are double displacement reactions in which one of the compounds formed is insoluble. This insoluble compound is called precipitate and it settles at the bottom.

           Redox Reactions

Those reactions in which simultaneous oxidation and reduction reactions take places.

Oxidation reactions: Those reactions which involves:

(i) Addition of oxygen

\[2{{H}_{2}}+{{O}_{2}}\to 2{{H}_{2}}O\]

Here hydrogen is oxidized.

(ii) Removal of hydrogen.

\[{{H}_{2}}S+{{I}_{2}}\to 2HI+S\]

Here hydrogen sulphide is oxidized

Reduction reaction: Those chemical reactions which involve

(i) Addition of hydrogen.

\[{{H}_{2}}S+{{I}_{2}}\to 2HI+S\]

(iii) Removal of hydrogen

\[ZnO+C\to Zn+CO\]

Here, Zinc Oxide is reduced.

Redox reaction: The reaction in which both reduction and oxidation takes place simultaneously is called redox reaction. e.g. \[ZnO+C\to Zn+CO\]

Oxidizing agents are those substances which can either donate oxygen or gain hydrogen.

Reducing agents are those substances which can either donate hydrogen or gain oxygen

\[Zn{{O}_{(s)}}+{{C}_{(s)}}\to Z{{n}_{(s)}}+C{{O}_{(g)}}\]

(Oxidizing agent) (Reducing agent)

Thus we can say that loss of 0 is reduction and loss of H oxidation.

\[{{H}_{2}}{{S}_{(g)}}+C{{l}_{2(g)}}\to {{S}_{(s)}}+2HC{{l}_{(g)}}\]