What is meant by the term "chemical reaction"? Write any three types of chemical reactions. How can we represent a chemical reaction?

Chemical Reaction

A chemical reaction is a process in which one or more substances (reactants) undergo a chemical change to form new substances (products) with different physical and chemical properties. During a chemical reaction, the bonds between atoms in the reactants are broken, and new bonds are formed to create products. This process is accompanied by the absorption or release of energy (exothermic or endothermic reactions).

C₃H₈+5O₂combustion3CO₂+4H₂O

Key characteristics of a chemical reaction include:

• Formation of new substances with distinct properties.
• Change in color, temperature, or state (solid, liquid, gas).
• Evolution of gas or precipitation (formation of a solid).

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Three Types of Chemical Reactions

1. Combination Reaction

   • Two or more reactants combine to form a single product.
   • Example: $2\mathrm{H}{}_2+\mathrm{O}{}_2\to 2\mathrm{H}{}_2\mathrm{O}$ (Hydrogen and oxygen combine to form water).

2. Decomposition Reaction

   • A single reactant breaks down into two or more simpler substances.
   • Example: $2\mathrm{H}{}_2\mathrm{O}\to 2\mathrm{H}{}_2+\mathrm{O}{}_2$ (Water decomposes into hydrogen and oxygen).

3. Displacement Reaction

   • An element displaces another element from its compound.
   • Example: $\mathrm{Zn}+\mathrm{CuSO}{}_4\to \mathrm{ZnSO}{}_4+\mathrm{Cu}$ (Zinc displaces copper from copper sulphate).

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Representation of a Chemical Reaction

A chemical reaction is represented using a chemical equation, which includes:

• Reactants (left side of the arrow).
• Products (right side of the arrow).
• Arrow (→ or ⇌) indicating the direction of the reaction.
• Balancing coefficients to ensure the number of atoms of each element is equal on both sides.

Example: $2\mathrm{Na}+2\mathrm{H}{}_2\mathrm{O}\to 2\mathrm{NaOH}+\mathrm{H}{}_2$ Here, sodium reacts with water to form sodium hydroxide and hydrogen gas.

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2Na+2H₂O2NaOH+H₂