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Class 10, Science, Chapter-1, Lecture-2, Types of Reaction (Notes)

COMBINATION REACTION:

A chemical reaction in which two or more substances combine to form a single substance is called a combination reaction.

Examples:

  1. Burning of coal.
    ${{\rm{C}}({\rm{s}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}})\buildrel {} \over
    \longrightarrow \,{\rm{C}}{{\rm{O}}_{\rm{2}}}({\rm{g}})}$
  2. Formation of water from Hydrogen and Oxygen
    ${2{{\rm{H}}_{\rm{2}}}({\rm{g}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}})\,\buildrel {} \over
    \longrightarrow \,2\,{{\rm{H}}_{\rm{2}}}{\rm{O}}({\rm{l}})}$
  3. Slaking of lime
    ${{\rm{CaO}}({\rm{s}}) + {{\rm{H}}_{\rm{2}}}{\rm{O}}({\rm{l}})\,\buildrel {} \over
    \longrightarrow {\rm{Ca}}{{({\rm{OH}})}_2}({\rm{aq}})}$

DECOMPOSITION REACTION:

A chemical reaction in which a compound breaks up into two or more simpler substances is called a decomposition reaction.

Examples:

  1. Ferrous sulphate crystals break, on heating, to give Ferric Oxide, Sulphur dioxide and Sulphur trioxide.
    $2{\rm{FeS}}{{\rm{O}}_{\rm{4}}}({\rm{s}})\buildrel {{\rm{Heat}}} \over
    \longrightarrow {\rm{F}}{{\rm{e}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}({\rm{s}}) + {\rm{S}}{{\rm{O}}_{\rm{2}}}({\rm{g}}) + {\rm{S}}{{\rm{O}}_{\rm{3}}}({\rm{g}}){\rm{ }}$
  2. Lime stone breaks, on heating, to give Quick Lime and Carbon dioxide gas.
    ${\rm{CaC}}{{\rm{O}}_{\rm{3}}}({\rm{s}})\buildrel {{\rm{Heat}}} \over
    \longrightarrow {\rm{CaO}}({\rm{s}}) + {\rm{C}}{{\rm{O}}_{\rm{2}}}({\rm{g}})$
  3. Lead Nitrate (white) breaks, on heating, to give Lead Oxide (orange), Nitrogen dioxide (brown fumes) and Oxygen.
    $2{\rm{Pb}}{({\rm{N}}{{\rm{O}}_{\rm{3}}})_2}({\rm{s}})\buildrel {{\rm{Heat}}} \over
    \longrightarrow 2{\rm{PbO}}({\rm{s}}) + 4{\rm{N}}{{\rm{O}}_{\rm{2}}}({\rm{g}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}})$
  4. Electrolysis of water
    $2{{\rm{H}}_{\rm{2}}}{\rm{O}}(l{\rm{)}}\buildrel {{\rm{Electric energy}}} \over
    \longrightarrow 2{{\rm{H}}_{\rm{2}}}({\rm{g}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}})$
  5. Photolysis of Silver chloride
    $2{\rm{AgCl}}({\rm{s}})\buildrel {{\rm{Light energy}}} \over
    \longrightarrow 2{\rm{Ag}}({\rm{s}}) + {\rm{C}}{{\rm{l}}_{\rm{2}}}({\rm{g}})$
  6. Photolysis of Silver bromide
    $2{\rm{AgBr}}({\rm{s}})\buildrel {{\rm{Light energy}}} \over
    \longrightarrow 2{\rm{Ag}}({\rm{s}}) + B{r_2}({\rm{g}})$

THERMAL DECOMPOSITION REACTION:

A chemical reaction in which a compound breaks up into two or more simpler substances due to heating is called a thermal decomposition reaction.

Examples:

  1. Ferrous sulphate crystals break, on heating, to give Ferric Oxide, Sulphur dioxide and Sulphur trioxide.
    $2{\rm{FeS}}{{\rm{O}}_{\rm{4}}}({\rm{s}})\buildrel {{\rm{Heat}}} \over
    \longrightarrow {\rm{F}}{{\rm{e}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}({\rm{s}}) + {\rm{S}}{{\rm{O}}_{\rm{2}}}({\rm{g}}) + {\rm{S}}{{\rm{O}}_{\rm{3}}}({\rm{g}}){\rm{ }}$
  2. Limestone breaks, on heating, to give Quick Lime and Carbon dioxide gas.
    ${\rm{CaC}}{{\rm{O}}_{\rm{3}}}({\rm{s}})\buildrel {{\rm{Heat}}} \over
    \longrightarrow {\rm{CaO}}({\rm{s}}) + {\rm{C}}{{\rm{O}}_{\rm{2}}}({\rm{g}})$
  3. Lead Nitrate (white) breaks, on heating, to give Lead Oxide (orange), Nitrogen dioxide (brown fumes) and Oxygen.
    $2{\rm{Pb}}{({\rm{N}}{{\rm{O}}_{\rm{3}}})_2}({\rm{s}})\buildrel {{\rm{Heat}}} \over
    \longrightarrow 2{\rm{PbO}}({\rm{s}}) + 4{\rm{N}}{{\rm{O}}_{\rm{2}}}({\rm{g}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}})$

EXOTHERMIC REACTION:

A chemical reaction in which net heat is released along with the formation of products is called an exothermic reaction. 

Examples:

  1. Burning of coal.
    ${\rm{C}}({\rm{s}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}})\buildrel {} \over
    \longrightarrow \,{\rm{C}}{{\rm{O}}_{\rm{2}}}({\rm{g}})$
  2. Formation of water from Hydrogen and Oxygen
    $2{{\rm{H}}_{\rm{2}}}({\rm{g}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}})\,\buildrel {} \over
    \longrightarrow \,2\,{{\rm{H}}_{\rm{2}}}{\rm{O}}({\rm{l}})$
  3. Slaking of lime
    ${\rm{CaO}}({\rm{s}}) + {{\rm{H}}_{\rm{2}}}{\rm{O}}({\rm{l}})\,\buildrel {} \over
    \longrightarrow {\rm{Ca}}{({\rm{OH}})_2}({\rm{aq}})$
  4. Burning of Natural Gas
    ${\rm{C}}{{\rm{H}}_{\rm{4}}}({\rm{g}}) + 2{{\rm{O}}_{\rm{2}}}({\rm{g}})\buildrel {} \over
    \longrightarrow {\rm{C}}{{\rm{O}}_{\rm{2}}}({\rm{g}}) + 2{{\rm{H}}_{\rm{2}}}{\rm{O}}\,({\rm{g}})$
  5. Respiration
    ${{\rm{C}}_{\rm{6}}}{{\rm{H}}_{{\rm{12}}}}{{\rm{O}}_{\rm{6}}}({\rm{aq}}) + 6\,{{\rm{O}}_{\rm{2}}}({\rm{aq}})\buildrel {} \over
    \longrightarrow 6{\rm{C}}{{\rm{O}}_{\rm{2}}}({\rm{aq}}) + 6{{\rm{H}}_{\rm{2}}}{\rm{O}}({\rm{l}})$
  6. Decomposition of vegetables into compost.

ENDOTHERMIC REACTION:

A chemical reaction in which net heat is absorbed along with the formation of products is called an endothermic reaction.

Examples:

  1. Nitrogen and Oxygen combine to form Nitrogen oxide and absorbs heat.
    ${{\rm{N}}_{\rm{2}}}({\rm{g}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}}) + \buildrel {{\rm{Heat}}} \over
    \longrightarrow \,2{\rm{NO}}({\rm{g}}){\rm{  }}$
  2. Ferrous sulphate crystals break, on heating, to give Ferric Oxide(red brown), Sulphur dioxide and Sulphur trioxide.
    $2{\rm{FeS}}{{\rm{O}}_{\rm{4}}}({\rm{s}})\buildrel {{\rm{Heat}}} \over
    \longrightarrow {\rm{F}}{{\rm{e}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}({\rm{s}}) + {\rm{S}}{{\rm{O}}_{\rm{2}}}({\rm{g}}) + {\rm{S}}{{\rm{O}}_{\rm{3}}}({\rm{g}}){\rm{ }}$
  3. Lime stone breaks, on heating, to give Quick Lime and Carbon dioxide gas.
    ${\rm{CaC}}{{\rm{O}}_{\rm{3}}}({\rm{s}})\buildrel {{\rm{Heat}}} \over
    \longrightarrow {\rm{CaO}}({\rm{s}}) + {\rm{C}}{{\rm{O}}_{\rm{2}}}({\rm{g}})$
  4. Lead Nitrate (white) breaks, on heating, to give Lead Oxide (orange), Nitrogen dioxide (brown fumes) and Oxygen.
    $2{\rm{Pb}}{({\rm{N}}{{\rm{O}}_{\rm{3}}})_2}({\rm{s}})\buildrel {{\rm{Heat}}} \over
    \longrightarrow 2{\rm{PbO}}({\rm{s}}) + 4{\rm{N}}{{\rm{O}}_{\rm{2}}}({\rm{g}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}})$