‘रचना-प्रयोग’ का मुख्य उद्देश्य क्या है?

व्याकरण का व्यावहारिक प्रयोग सिखाना

‘द्वितीयः’ किस प्रकार की संख्या है?

क्रमवाचक (दूसरा)

Why must a chemical equation be balanced?

Because matter is conserved — atoms are neither created nor destroyed, so the number of atoms of each element must be equal on both sides.

Why is respiration considered an exothermic reaction?

Because the breakdown of glucose during respiration releases energy, which the body uses to stay warm and do work.

What is a chemical reaction? Give one everyday example.

A change in which reactants are converted into new substances (products) with different properties; for example, the rusting of iron or the souring of milk.

What information does a balanced chemical equation give?

It shows the reactants and products, their physical states, and the relative number of atoms/molecules, while obeying the law of conservation of mass.

Define a combination reaction with an example.

A reaction in which two or more substances combine to form a single product, e.g. calcium oxide reacting with water to form calcium hydroxide.

What is a decomposition reaction? Name its three types.

A reaction in which a single compound breaks into two or more simpler substances, brought about by heat (thermal), light (photolytic) or electricity (electrolytic).

Distinguish between displacement and double displacement reactions.

In displacement, a more reactive element replaces a less reactive one from its compound; in double displacement, two compounds exchange ions, often forming a precipitate.

What are oxidation and reduction in terms of oxygen and hydrogen?

Oxidation is the gain of oxygen or loss of hydrogen; reduction is the loss of oxygen or gain of hydrogen. Both occur together in a redox reaction.

What is corrosion, and how can rusting of iron be prevented?

Corrosion is the slow eating away of a metal by reaction with air and moisture; rusting is prevented by painting, oiling, greasing, galvanising or coating with a less reactive metal.

What is rancidity, and how can it be slowed down?

Rancidity is the oxidation of fats and oils in food, spoiling its taste and smell; it is slowed by adding antioxidants, refrigeration, airtight packing or flushing with nitrogen.

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Chapter 1: Chemical Reactions and EquationsClass 10 Science — summary, notes, extra questions & NCERT solutions

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A chemical equation is balanced to satisfy which law?

Summary

Chemical reactions remake substances: bonds in the reactants break and new bonds form, producing products with new properties. A chemical equation is the shorthand for that change, and it must be balanced so that every element has the same number of atoms on both sides — a direct consequence of the law of conservation of mass. Reactions are grouped by what happens to the substances: combination (reactants join into one product), decomposition (one substance splits into many under heat, light or electricity), displacement (a more reactive element pushes out a less reactive one) and double displacement (two compounds exchange ions, often forming a precipitate). Many reactions are redox reactions, where oxidation and reduction happen together. Everyday processes like the rusting of iron (corrosion) and the spoiling of fried food (rancidity) are slow oxidation reactions you can learn to recognise and prevent.

Chemical equations and balancingCombination and decomposition reactionsDisplacement and double displacementOxidation and reduction (redox)Corrosion and rancidity

Key terms

Balanced equation

An equation with equal atoms of each element on both sides.

Combination reaction

Two or more reactants form a single product.

Decomposition reaction

A single reactant breaks into two or more products.

Redox reaction

Oxidation and reduction occurring simultaneously.

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An equation with equal atoms of each element on both sides.

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Chapter 1: Chemical Reactions and EquationsClass 10 Science — summary, notes, extra questions & NCERT solutions

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Key terms

Extra questions & answers

Activity 1.1

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