(b) Displacement reaction & a neutralization reaction.ĭirect combination : “When two substances react chemically to form a new substance which is a compound, it is a direct combination reaction”ĭecomposition reaction : “When a compound breaks up or decomposed into two or more substances which are simpler and can sustain independently”.ĭisplacement reaction : “When an element displaces another element in a compound during a chemical reaction, it is a displacement reaction.” (a) Direct combination reaction & a decomposition reaction Hydrogen (a gas) + Oxygen (a gas) combines to form water (liquid). Therefore direct combination is also called ‘synthesis reaction’. When two or more substances combine to form a new compound with new Chemical properties. State why a direct combination reaction is called a – ‘synthesis reaction’. Thermal decomposition of mercury oxides : Thermal decomposition of mercury oxide – The colour of mercury changes from red to silvery, that is metallic.Addition of water to quick lime : Addition of water to quicklime – The solution boils and heat is produced accompanied by a hissing sound.hydrochloric acid to silver nitrate : Addition of dilute hydrochloric acid to silver nitrate – A white coloured precipitate is formed which is AgCl acid to an active metal : addition of dilute acid to an active metal – The test tube becomes hot and hydrogen gas is evolved, which means heat is produced. (iv) Thermal decomposition of mercury oxide.Ĭhemical reaction : “A chemical reaction is a chemical change where substances react with each other to form a new substance.” (ii) Addition of dilute hydrochloric acid to silver nitrate (i) Addition of dilute acid to an active metal With reference to each of the above indications, state the external indication seen during – A chemical reaction is often accompanied by external indications or characteristics which include – Chemical Reactions Class-8 Dalal ICSE New Simplified Chemistry Dr Viraf J Dalal Middle School Allied Publishers Solutions. Visit official Website CISCE for detail information about ICSE Board Class-8. We Provide Step by Step Solutions of Exercise/Lesson -6 Chemical Reactions with Objective Type Questions, Fill in the blanks and Give reason, Match the following of Dr Viraf J Dalal Middle School Chemistry Allied Publishers. Class-8 Dalal Simplified Chemical Reactions ICSE Chemistry Dr Viraf J Dalal Middle School Allied Publishers Solutions.