Chemical Changes and Reactions
ICSE · Class 9 · Chemistry
Complete topic list for Chemical Changes and Reactions in ICSE Class 9 Chemistry. Key concepts, sub-topics, and what to focus on for board exams.
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1. Chemical Reaction and Its Signs
- A chemical reaction is the process of breaking the chemical bonds of the reactants and making new bonds to form new products.
- A chemical bond is the force that holds the atoms of a molecule together, as in a compound.
- Chemical reactions occur when particles collide, usually by close contact or by supply of energy.
2. Types of Chemical Reactions
- The main types of chemical reactions are direct combination, decomposition, displacement, and double decomposition.
- In a combination reaction, two or more substances combine to form a single product.
- In a decomposition reaction, a compound breaks into simpler substances or elements.
3. Decomposition, Reversible Reactions, and Thermal Dissociation
- Decomposition can happen by heat, light, or electricity.
- Thermal decomposition is decomposition brought about by heat.
- Thermal dissociation is a simultaneous reversible decomposition reaction brought about only by heat.
4. Catalysts, Promoters, and Activity Series
- Catalysts speed up or slow down the rate of reactions, but catalysts themselves do not take part in the reaction.
- When a catalyst accelerates a reaction, it is a positive catalyst.
- A catalyst employed to retard a reaction is a negative catalyst.
Key Concepts
Central concept: Chemical change is the breaking of old bonds and formation of new bonds that creates new substances, often with energy change and observable signs such as gas, colour change, precipitate, or change of state.
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