Class 10 Chemistry Chapter 1: Chemical Reactions and Equations

A chemical reaction is a process where reactants undergo a chemical change to form completely new products with new properties. Signs of a reaction: Change in state, change in color, evolution of a gas, or change in temperature.

According to the Law of Conservation of Mass, mass can neither be created nor destroyed in a chemical reaction. Therefore, the number of atoms of each element on the reactant side must be exactly equal to the number of atoms on the product side. We achieve this by multiplying the formulas by whole numbers (coefficients).

• Combination Reaction: Two or more reactants combine to form a single product. (e.g., $C + O_2 \rightarrow CO_2$).
• Decomposition Reaction: A single reactant breaks down to form two or more products upon heating, light, or electricity. (e.g., $CaCO_3 \xrightarrow{\text{Heat}} CaO + CO_2$).
• Displacement Reaction: A more reactive element displaces a less reactive element from its salt solution. (e.g., $Fe + CuSO_4 \rightarrow FeSO_4 + Cu$).
• Double Displacement Reaction: Two ionic compounds exchange their ions to form two new compounds, often forming a precipitate. (e.g., $Na_2SO_4 + BaCl_2 \rightarrow BaSO_4 \downarrow + 2NaCl$).

• Oxidation: The gain of oxygen or the loss of hydrogen.
• Reduction: The loss of oxygen or the gain of hydrogen. When both happen simultaneously in a reaction, it is called a Redox Reaction.