write down all five characteristic of chemical reactions
Answers
1) Change of colour - When citric acid is added to Potassium permangenate then the purple colour starts discharging .
2)Change of state - When hydrogen(gas) reacts with oxygen(gas) , they form water a liquid
3)Evolution of a gas - When lead nitrate is heated the it decomposes to lead oxide , nitrogen dioxide with oxygen .
4) Formation of a precipitate - When lead nitrate reacts with potassium iodide , it forms a yellow precipitate Lead iodide and potassium nitrate .
5)Change in temperature -
- Exothermic reaction - reaction in which heat is released
When quick lime reacts with water to form slaked lime , it releases a lot of energy .
- Endothermic reaction - reaction in which heat is absorbed
When hydrogen reacts with iodine to form hydrogen iodide , it absorbs a lot of energy .
1)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.