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¢ 1. Chemical Reaction A process in which one or more substances (reactants) change into new substances (products). & Example: Mg +Q, — MgO ¢ 2. Chemical Equation Representation of a chemical reaction using symbols and formulas. Types: Word Equation: Magnesium + Oxygen — Magnesium Oxide Skeletal Equation: Mg + 0, + MgO Balanced Equation: 2Mg + 0, - 2MgQ ¢ 3. Balanced Chemical Equation Equation with equal number of atoms on both sides. o Law Used: Law of Conservation of Mass — Mass is neither created nor destroyed. ¢ 4, Steps to Balance Equation Write skeletal equation List atoms on both sides Balance metals — non-metals — oxygen — hydrogen Check final balance ¢ 5. Types of Chemical Reactions (i) Combination Reaction Two or more substances combine to form one product. @& CaO +H,0 - Ca(OH), (ii) Decomposition Reaction A compound breaks into simpler substances. & CaCO, — Cad +0, Types: Thermal (heat) Electrolytic (electricity) Photolytic (light) (iii) Displacement Reaction More reactive element displaces less reactive one. & Zn+ CuSO, = ZnSO, +Cu (iv) Double Displacement Reaction Exchange of ions between compounds. & Na,SO, + BaCl, — BaSO, + 2NaCl & Includes: Precipitation Reaction (solid formed) ¢ 6. Oxidation and Reduction » Oxidation: Gain of oxygen OR loss of hydrogen y Reduction: Loss of oxygen OR gain of hydrogen & Example: CuO +H, = Cu+H,0 CuO -. reduced H, + oxidized & Both occur together = Redox Reaction + 7. Effects of Oxidation in Daily Life (i) Corrosion Slow destruction of metals by air/moisture. o& Example: Rusting of iron (ii) Rancidity Oxidation of fats/oils — bad smell & taste ér Prevention: Use antioxidants Store in airtight containers Refrigeration + 8. Exothermic & Endothermic Reactions @ Exothermic Reaction Heat is released @& CH,+0, — CO, +H,0 + Heat S< Endothermic Reaction Heat is absorbed & Caco, — Ca0+C0O, ¢ 9. Important Indicators of Chemical Reaction Change in colour Change in temperature Gas formation Precipitate formation + 10. Key Examples to Remember Rusting — Oxidation Photosynthesis — Endothermic Respiration — Exothermic ® Quick Revision Tricks OILRIG — Oxidation Is Loss, Reduction Is Gain Always balance equation — important for exams Identify reaction type from pattern 
