Chemical Reactions and Equations Class 10 Notes

 

Class 10 Science Chapter 1: Chemical Reactions and Equations – Short Notes

1. Chemical Reactions:

A chemical reaction occurs when one or more substances react to form new substances with different properties.

• Reactants: Substances that undergo the reaction.
• Products: New substances formed after the reaction.

2. Characteristics of Chemical Reactions:

Chemical reactions involve:

• Change in state: Solid to liquid or gas (e.g., ice melting).
• Change in color: (e.g., rusting of iron).
• Evolution of gas: (e.g., hydrogen gas released in reaction with metals).
• Change in temperature: Exothermic (releases heat) or Endothermic (absorbs heat).
• Formation of precipitate: Insoluble solid is formed (e.g., reaction between barium chloride and sulfuric acid).

3. Chemical Equations:

A chemical equation represents a chemical reaction using symbols and formulas.

• Word equation: Represents reaction using words (e.g., Magnesium + Oxygen → Magnesium oxide).
• Balanced chemical equation: The number of atoms of each element is the same on both sides of the equation (e.g., $2Mg+O_2\to 2MgO$).

Steps to balance a chemical equation:

• Write the skeletal equation.
• Balance each element one by one.
• Adjust coefficients, never change subscripts in formulas.

4. Types of Chemical Reactions:

• Combination Reaction: Two or more substances combine to form a new substance (e.g., $2H_2+O_2\to 2H_{2}O$).
• Decomposition Reaction: A compound breaks down into two or more simpler substances (e.g., $2H_2{O}_2\to 2H_{2}O+O_2$).
• Displacement Reaction: A more reactive element displaces a less reactive element from its compound (e.g., $Zn+CuS{O}_4\to ZnS{O}_4+Cu$).
• Double Displacement Reaction: Exchange of ions between two compounds to form new compounds (e.g., $N{a}_{2}S{O}_4+BaC{l}_2\to BaS{O}_4+2NaCl$).
• Redox Reaction: Involves both oxidation (loss of electrons) and reduction (gain of electrons) simultaneously.

5. Oxidation and Reduction:

• Oxidation: Gain of oxygen or loss of hydrogen (e.g., $Cu\to CuO$).
• Reduction: Loss of oxygen or gain of hydrogen (e.g., $CuO\to Cu$).

6. Corrosion and Rancidity:

• Corrosion: The gradual destruction of metals by chemical reactions with the environment (e.g., rusting of iron).
• Rancidity: The oxidation of fats and oils when exposed to air, leading to foul smell and taste. Prevented by storing food in airtight containers or refrigeration.