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:
- Burning of coal.
${{\rm{C}}({\rm{s}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}})\buildrel {} \over
\longrightarrow \,{\rm{C}}{{\rm{O}}_{\rm{2}}}({\rm{g}})}$ - Formation of water from Hydrogen and Oxygen
${2{{\rm{H}}_{\rm{2}}}({\rm{g}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}})\,\buildrel {} \over
\longrightarrow \,2\,{{\rm{H}}_{\rm{2}}}{\rm{O}}({\rm{l}})}$ - 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:
- Ferrous sulphate crystals break, on heating, to give Ferric Oxide, Sulphur dioxide and Sulphur trioxide.
$2{\rm{FeS}}{{\rm{O}}_{\rm{4}}}({\rm{s}})\buildrel {{\rm{Heat}}} \over
\longrightarrow {\rm{F}}{{\rm{e}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}({\rm{s}}) + {\rm{S}}{{\rm{O}}_{\rm{2}}}({\rm{g}}) + {\rm{S}}{{\rm{O}}_{\rm{3}}}({\rm{g}}){\rm{ }}$ - Lime stone breaks, on heating, to give Quick Lime and Carbon dioxide gas.
${\rm{CaC}}{{\rm{O}}_{\rm{3}}}({\rm{s}})\buildrel {{\rm{Heat}}} \over
\longrightarrow {\rm{CaO}}({\rm{s}}) + {\rm{C}}{{\rm{O}}_{\rm{2}}}({\rm{g}})$ - Lead Nitrate (white) breaks, on heating, to give Lead Oxide (orange), Nitrogen dioxide (brown fumes) and Oxygen.
$2{\rm{Pb}}{({\rm{N}}{{\rm{O}}_{\rm{3}}})_2}({\rm{s}})\buildrel {{\rm{Heat}}} \over
\longrightarrow 2{\rm{PbO}}({\rm{s}}) + 4{\rm{N}}{{\rm{O}}_{\rm{2}}}({\rm{g}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}})$ - Electrolysis of water
$2{{\rm{H}}_{\rm{2}}}{\rm{O}}(l{\rm{)}}\buildrel {{\rm{Electric energy}}} \over
\longrightarrow 2{{\rm{H}}_{\rm{2}}}({\rm{g}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}})$ - Photolysis of Silver chloride
$2{\rm{AgCl}}({\rm{s}})\buildrel {{\rm{Light energy}}} \over
\longrightarrow 2{\rm{Ag}}({\rm{s}}) + {\rm{C}}{{\rm{l}}_{\rm{2}}}({\rm{g}})$ - 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:
- Ferrous sulphate crystals break, on heating, to give Ferric Oxide, Sulphur dioxide and Sulphur trioxide.
$2{\rm{FeS}}{{\rm{O}}_{\rm{4}}}({\rm{s}})\buildrel {{\rm{Heat}}} \over
\longrightarrow {\rm{F}}{{\rm{e}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}({\rm{s}}) + {\rm{S}}{{\rm{O}}_{\rm{2}}}({\rm{g}}) + {\rm{S}}{{\rm{O}}_{\rm{3}}}({\rm{g}}){\rm{ }}$ - Limestone breaks, on heating, to give Quick Lime and Carbon dioxide gas.
${\rm{CaC}}{{\rm{O}}_{\rm{3}}}({\rm{s}})\buildrel {{\rm{Heat}}} \over
\longrightarrow {\rm{CaO}}({\rm{s}}) + {\rm{C}}{{\rm{O}}_{\rm{2}}}({\rm{g}})$ - 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:
- Burning of coal.
${\rm{C}}({\rm{s}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}})\buildrel {} \over
\longrightarrow \,{\rm{C}}{{\rm{O}}_{\rm{2}}}({\rm{g}})$ - Formation of water from Hydrogen and Oxygen
$2{{\rm{H}}_{\rm{2}}}({\rm{g}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}})\,\buildrel {} \over
\longrightarrow \,2\,{{\rm{H}}_{\rm{2}}}{\rm{O}}({\rm{l}})$ - Slaking of lime
${\rm{CaO}}({\rm{s}}) + {{\rm{H}}_{\rm{2}}}{\rm{O}}({\rm{l}})\,\buildrel {} \over
\longrightarrow {\rm{Ca}}{({\rm{OH}})_2}({\rm{aq}})$ - Burning of Natural Gas
${\rm{C}}{{\rm{H}}_{\rm{4}}}({\rm{g}}) + 2{{\rm{O}}_{\rm{2}}}({\rm{g}})\buildrel {} \over
\longrightarrow {\rm{C}}{{\rm{O}}_{\rm{2}}}({\rm{g}}) + 2{{\rm{H}}_{\rm{2}}}{\rm{O}}\,({\rm{g}})$ - Respiration
${{\rm{C}}_{\rm{6}}}{{\rm{H}}_{{\rm{12}}}}{{\rm{O}}_{\rm{6}}}({\rm{aq}}) + 6\,{{\rm{O}}_{\rm{2}}}({\rm{aq}})\buildrel {} \over
\longrightarrow 6{\rm{C}}{{\rm{O}}_{\rm{2}}}({\rm{aq}}) + 6{{\rm{H}}_{\rm{2}}}{\rm{O}}({\rm{l}})$ - 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:
- Nitrogen and Oxygen combine to form Nitrogen oxide and absorbs heat.
${{\rm{N}}_{\rm{2}}}({\rm{g}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}}) + \buildrel {{\rm{Heat}}} \over
\longrightarrow \,2{\rm{NO}}({\rm{g}}){\rm{ }}$ - Ferrous sulphate crystals break, on heating, to give Ferric Oxide(red brown), Sulphur dioxide and Sulphur trioxide.
$2{\rm{FeS}}{{\rm{O}}_{\rm{4}}}({\rm{s}})\buildrel {{\rm{Heat}}} \over
\longrightarrow {\rm{F}}{{\rm{e}}_{\rm{2}}}{{\rm{O}}_{\rm{3}}}({\rm{s}}) + {\rm{S}}{{\rm{O}}_{\rm{2}}}({\rm{g}}) + {\rm{S}}{{\rm{O}}_{\rm{3}}}({\rm{g}}){\rm{ }}$ - Lime stone breaks, on heating, to give Quick Lime and Carbon dioxide gas.
${\rm{CaC}}{{\rm{O}}_{\rm{3}}}({\rm{s}})\buildrel {{\rm{Heat}}} \over
\longrightarrow {\rm{CaO}}({\rm{s}}) + {\rm{C}}{{\rm{O}}_{\rm{2}}}({\rm{g}})$ - Lead Nitrate (white) breaks, on heating, to give Lead Oxide (orange), Nitrogen dioxide (brown fumes) and Oxygen.
$2{\rm{Pb}}{({\rm{N}}{{\rm{O}}_{\rm{3}}})_2}({\rm{s}})\buildrel {{\rm{Heat}}} \over
\longrightarrow 2{\rm{PbO}}({\rm{s}}) + 4{\rm{N}}{{\rm{O}}_{\rm{2}}}({\rm{g}}) + {{\rm{O}}_{\rm{2}}}({\rm{g}})$