Question

Explain the characteristic features of changes in a chemical reaction with examples

Answer 1

Answer:

Some signs that a chemical change occurred include temperature increase, spontaneous change in color after mixing compounds, a marked odor after the reaction begins, formation of a precipitate in the solution and release of bubbles.

Examples - Endothermic Reaction, Exothermic Reaction, spontaneous reaction etc

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Answer 2

Answer:

Evolution of gas

Some chemical reactions are characterised by the evolution of gas.

For Ex:1)Reaction between zinc and dilute sulphuric acid to form hydrogen gas.

2)Reaction between sodium carbonate and dilute hydrochloric acid to form carbon dioxide gas.

2)Formation of precipitate

Some chemical reactions are characterised by the formation of precipitate.

For Ex:1)Reaction between Potassium iodide and lead nitrate to form yellow precipitate of lead iodide.

2)Reaction between sulphuric acid and barium chloride to form white precipitate of barium sulphate.

3)Change in colour

Some chemical reactions are characterised by change in colour

For Ex:1)When citric acid reacts with potassium permanganate (purple) then purple colour disappears

2)When sulphur dioxide gas reacts with acidified potassium dichromate,change in colour from orange to yellow is observed.

4)Change in temperature

Those reactions in which heat is produced or evolved are called exothermic reactions.

For Ex:Reaction between zinc granules with dilute sulphuric acid.

Those reactions in which heat is absorbed are called as endothermic reactions.

Reaction between barium hydroxide and ammonium chloride to form barium chloride,ammonia and water.

5)Change of state

Some chemical reactions are characterised by change in state.

For Ex:when wax(solid) is burned ,then water(liquid) and carbon dioxide(gas) are formed.

 

Explanation: