Class 10 / Science
Class 10 Science Chemical Reactions Notes
Revision notes on chemical reactions, equations, balancing, and reaction types.
Topic introduction
Chemical Reactions and Equations is the foundation chapter for Class 10 Chemistry. It teaches how reactions are represented, why equations are balanced, and how to identify common reaction types from reactants and products.
Key points
- A chemical equation represents a chemical reaction using symbols and formulae.
- Equations must be balanced to follow conservation of mass.
- Common reaction types include combination, decomposition, displacement, and double displacement.
Definitions
Chemical reaction: A process in which one or more substances change to form new substances.
Chemical equation: A symbolic representation of a chemical reaction using formulae and symbols.
Balanced equation: An equation in which the number of atoms of each element is equal on both sides.
Oxidation: Addition of oxygen or removal of hydrogen from a substance.
Reduction: Removal of oxygen or addition of hydrogen to a substance.
Examples
- 2H2 + O2 -> 2H2O is a balanced equation.
- CaO + H2O -> Ca(OH)2 is a combination reaction.
- A white precipitate in a reaction can be evidence of a chemical change.
- Rancidity is oxidation of fats and oils that changes smell and taste.
Balancing equations
Count atoms of each element on both sides of the equation.
Change coefficients, not chemical formulae, to balance the equation.
Identifying reactions
In combination reactions, two or more substances form one product.
In decomposition reactions, one compound breaks down into simpler substances.
In displacement reactions, a more reactive element displaces a less reactive element from its compound.
Common mistakes
- Changing subscripts in chemical formulae while balancing equations.
- Calling every reaction with two reactants a combination reaction without checking products.
- Forgetting physical states when the question asks for a complete chemical equation.
- Mixing up oxidation and reduction.
- Writing signs of reaction without observation words such as gas evolved, colour change, temperature change, or precipitate formed.
Quick practice
- Why should chemical equations be balanced?
- Identify the type of reaction: A + B -> AB.
- Write one sign that a chemical reaction has occurred.
Related practice
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