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Eduvista · Class 10 Science

Chemical Reactions and Equations

A focused lesson and practice set. This page covers the concepts listed below; it is not a claim of complete chapter or syllabus coverage.

Learn the essentials

What changes in a reaction?

Reactants rearrange their atoms to form products. A reaction may show a colour change, gas, precipitate, temperature change or change of state. An observation alone does not identify every product.

Balance by counting atoms

The number of atoms of each element must match on both sides. Change coefficients before formulas; changing a subscript changes the substance.

Recognise the pattern

Combination forms one product; decomposition breaks one reactant apart; displacement replaces an element; double displacement exchanges ions. Oxidation and reduction occur together.

Worked example

Balance magnesium reacting with oxygen to form magnesium oxide.

  1. Write Mg + O₂ → MgO.
  2. Put 2 before MgO to balance oxygen: Mg + O₂ → 2MgO.
  3. Put 2 before Mg: 2Mg + O₂ → 2MgO. Check Mg: 2 = 2; O: 2 = 2.

Memory trick

Count atoms in a two-column tally. Balance the element appearing in the fewest formulas first; leave hydrogen and oxygen until later when practical.

Common mistakes

  • Changing MgO to MgO₂ to make oxygen balance.
  • Calling rusting only a colour change; it is oxidation and corrosion.
  • Forgetting state symbols when the question asks for them.

Practice recall

Tap a card to reveal the answer. These are original Eduvista study cards.

Original practice quiz

Choose one answer per question. You can change it and see why it is right or wrong.

0 of 2 answered · 0 correct
1. Which equation is balanced?
2. Why must you not change a subscript while balancing?

Quick revision sheet

  • Atoms are conserved in a balanced equation.
  • Combination: A + B → AB; decomposition: AB → A + B.
  • Oxidation can involve gain of oxygen or loss of hydrogen; reduction is the reverse.
  • Rancidity is oxidation of fats and oils; airtight storage slows it.

Original Eduvista explanations and practice aligned to the named NCERT topic. Check your current textbook and school syllabus for the full prescribed scope. NCERT textbooks ↗

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