Introduction
- Chemical reaction: Process where reactants transform into products with new chemical properties.
- Examples:
- Combustion: C + O₂ → CO₂
- Rusting: Fe + O₂ + H₂O → Fe₂O₃·xH₂O
Types of Chemical Reactions
- Combination Reaction (Synthesis)
- Two or more substances combine to form a single product
- Example: 2H₂ + O₂ → 2H₂O
- Decomposition Reaction
- A single compound breaks into two or more simpler substances
- Example: 2HgO → 2Hg + O₂
- Displacement Reaction
- More reactive element displaces a less reactive element from its compound
- Example: Zn + CuSO₄ → ZnSO₄ + Cu
- Double Displacement Reaction
- Exchange of ions between two compounds
- Example: AgNO₃ + NaCl → AgCl + NaNO₃
- Redox Reaction (Oxidation–Reduction)
- Oxidation: Loss of electrons
- Reduction: Gain of electrons
- Example: Zn + Cu²⁺ → Zn²⁺ + Cu
- Neutralization Reaction
- Acid reacts with base to form salt and water
- Example: HCl + NaOH → NaCl + H₂O
- Exothermic and Endothermic Reactions
- Exothermic: Release energy (e.g., combustion)
- Endothermic: Absorb energy (e.g., photosynthesis)
Chemical Equations
- Chemical equation: Representation of a chemical reaction using symbols and formulas.
- Balanced chemical equation: Number of atoms of each element is same on both sides.
Steps to Balance Chemical Equations
- Write reactants and products.
- Count atoms of each element.
- Use coefficients to balance atoms.
- Check that all atoms are balanced.
Example:
Unbalanced: H₂ + O₂ → H₂O
Balanced: 2H₂ + O₂ → 2H₂O
Important Concepts
- Reactants and Products:
- Reactants → Substances initially present
- Products → New substances formed
- Indicators of Chemical Reactions:
- Gas evolution, color change, temperature change, precipitate formation
- Conservation of Mass:
- Mass of reactants = Mass of products