Class 10 Science: Chemical Reactions and Equations — a simple summary

A chemical reaction happens when one or more substances change into new substances with different properties. You can spot a reaction by the signs: a change in colour, a change in state, a gas being given off, a change in temperature, or a precipitate (a solid) forming. The starting substances are the reactants; the new substances formed are the products.

Chemical equations

A chemical equation is just a short way of writing a reaction, using symbols and formulae. For example, when magnesium burns in air:

Mg + O₂ → MgO

The arrow means "changes into" and points from reactants to products.

Why we balance equations

By the law of conservation of mass, matter is neither created nor destroyed in a reaction — so the number of atoms of each element must be the same on both sides. The equation above is not balanced: there are two oxygen atoms on the left but only one on the right. Balancing fixes this:

2Mg + O₂ → 2MgO

Now there are 2 magnesium and 2 oxygen atoms on each side. We balance by adding numbers (coefficients) in front of formulae — never by changing the formulae themselves.

Types of chemical reactions

• ✓ Combination: two or more substances join to form one product. e.g. CaO + H₂O → Ca(OH)₂.
• ✓ Decomposition: one substance breaks into two or more. It needs energy — heat, light or electricity. e.g. heating calcium carbonate: CaCO₃ → CaO + CO₂.
• ✓ Displacement: a more reactive element pushes out a less reactive one. e.g. Fe + CuSO₄ → FeSO₄ + Cu.
• ✓ Double displacement: two compounds swap partners, often forming a precipitate. e.g. Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl.

Oxidation, reduction and redox

Oxidation is the gain of oxygen (or loss of hydrogen); reduction is the loss of oxygen (or gain of hydrogen). When both happen together in one reaction, it is a redox reaction. A handy memory aid is OIL RIG — Oxidation Is Loss, Reduction Is Gain (of electrons). Everyday examples include the rusting of iron and the corrosion of metals, and food turning stale when fats and oils are oxidised (rancidity).

Want this taught aloud in your language?

Balancing equations and telling reaction types apart click faster when explained with examples your child can picture. Upload this NCERT chapter to Tutorfic and it will teach it aloud in your child's language, then quiz them on balancing and reaction types with the reasoning behind each answer. It's one of all the Class 10 subjects Tutorfic teaches.