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- Any process that involves the rearrangement of the structure of the substance or conversion of reactants into products is defined as a Chemical Reaction
- In a chemical reaction the nature and the identity of any substance change.
- Some common examples of such change from everyday life are:
- Formation of curd from milk. (Lactose present in milk is converted into lactic acid by the action of bacteria.)
- Rusting of iron nails or iron rods or pans when exposed to the humid atmosphere. (Iron gets converted into oxides of iron i.e., rust when exposed to water and oxygen).
- Fermentation of grapes (glucose present in grapes gets converted into alcohol and carbon dioxide gas by action of yeast).
- Digestion of food in our body. (Complex food i.e., sucrose is broken down into simpler particles like glucose)
- Our respiration process generates energy.
- Glucose in the presence of oxygen broken down to release energy along with carbon dioxide and water.
- Photosynthesis is done by plants.
- Carbon dioxide and water combine in the presence of sunlight and chlorophyll to form glucose.
- A complete chemical equation represents the reactants, products and their physical states symbolically.
- A chemical equation is balanced so that the numbers of atoms of each type involved in a chemical reaction are the same on the reactant and product sides of the equation. Equations must always be balanced.
- In a combination reaction, two or more substances combine to form a new single substance.
- Decomposition reactions are opposite to combination reactions. In a decomposition reaction, a single substance decomposes to give two or more substances.
- Reactions in which heat is given out along with the products are called exothermic reactions.
- Reactions in which energy is absorbed are known as endothermic reactions.
- When an element displaces another element from its compound, a displacement reaction occurs.
- Two different atoms or groups of atoms (ions) are exchanged in double displacement reactions.
- Precipitation reactions produce insoluble salts.
- Reactions also involve the gain or loss of oxygen or hydrogen by substances.
- Oxidation is the gain of oxygen or loss of hydrogen. Reduction is the loss of oxygen or the gain of hydrogen.