On this page, we revise our chapter chemical reactions and equation with pointwise short Notes that help you revise your whole chapter all the topics are covered.
Chemical Reactions and Equation Short Revision Notes
1. All chemical changes are accompanied by chemical reactions.
2. In a chemical reaction, the reacting species i.e. atoms, ions or molecules combine under suitable conditions to form product species.
3. All chemical reactions can be represented with the help of chemical equations. These may be both word equations and symbol equations.
4. Word equations do not give true pictures of the chemical reactions. Symbol equations are considered to be better.
5. Symbol equations are always written from the word equations.
6. A symbol equation can be balanced by equating the atoms of different elements on both sides in terms of their number as well as mass.
7. A chemical equation has to be balanced to fulfil the requirement of the law of conservation of mass which means that the total mass of the reactant species is the same as the total mass of the product species in a chemical reaction.
8. Balancing of chemical equations can be done by Hit and Trial Method which is carried in steps.
9. Chemical equations can be made more informative by writing state symbols of reactants and products, by indicating the gas evolved with an arrow pointing upwards and the precipitate formed with an arrow pointing downwards.
10. Chemical reactions are in general accompanied by heart energy changes. These are called exothermic and endothermic reactions.
11. In exothermic reactions, the heat evolved is indicated by the plus(+) sign and in endothermic reactions heat is absorbed by the minus (-) sign on the product side.
12. Chemical reactions are classified into various types depending upon the mode of the combination of reactants.
13. In combination reactions, two or more substances combine under suitable conditions to form a single substance.
14. Combination reactions are also known as synthesis.
15. Decomposition reactions are opposite to the combination reactions. In these reactions, a single substance decomposes under suitable conditions to form two or more substances.
16. In displacement reactions, one element takes the position of another element in a compound.
17. Normally a more reactive element displaces a less reactive element present in a compound.
18. In double displacement reactions, one component of both the reactants gets displaced to form the products.
19. Double displacement reactions are generally of ionic nature taking place in an aqueous solution. Acid-base nutrition reactions are double displacement or ionic in nature.
20. In an oxidation reaction, a substance either gains oxygen or loses hydrogen. The reverse is the case in a reduction reaction.
21. The substance undergoing oxidation is called a reducing agent while the substance undergoing reduction is known as an oxidizing agent.
22. In the terms of electronic concept, oxidation represents the loss of one or more electrons from a compound while reduction represents the gain of one or more electrons by a compound in a chemical reaction.
23. All combustion reactions are basically oxidation reactions. They may or may not be accompanied by flame.
24. Respiration taking place in cells of all living beings is an oxidation reaction.
25. Corrosion is the chemical process involving the slow eating of the surfaces of certain metals when exposed to the atmosphere for a long time. In the case of iron, corrosion is known as rusting.
26. Rust is a substance that is soft and porous in nature. It is brown in colour and has the chemical formula Fe₂O₃⋅xH₂O
27. Rancidity is the slow oxidation of certain oils or fats present in food materials resulting in a foul smell.