Chemical Reactions and Equations- Quick Revision Notes Class 10

Chemical Reactions and Equations is chapter 1 of class 10 Science of RBSE and one of the most important chapters for board exams.

Here you will find quick revision notes in easy language for fast learning and last-minute revision. After  reading these notes, you can also go through the Questions of Chemical Reactions and Equations and practice MCQs for better understanding. 

What is a Chemical Reaction?

A chemical reaction is a process in which one or more substance (reactants) change into new substances(product) with different properties.

Example

Mg + O₂ →MgO

How to Identify a Chemical Reaction?

A chemical reaction has occurred if you observe;

i.              Change in colour

ii.          Change in temperature

iii.       Formation of gas

iv.        Formation of precipitate

v.           Change in state

What is Chemical Equation?

A chemical equation is a symbolic representation of a chemical reaction using chemical formulas and symbols. It shows the reactants, products, and the direction of the reaction.

Types of Chemical Equation

i.  Word equation

 Names of reactants and products are written.

   Magnesium + oxygen →Magnesium oxide

ii.   Skeletal equation or unbalanced equation

  Formula and symbols of reactants and products are written.

    Mg + O₂ →MgO

iii.    Balanced equation

 Equal numbers of atoms of reactants and products on both sides according to the Law of conservation of mass.

    2Mg + O₂ →2MgO

Physical states and special conditions should be written

Solid – (s)

Liquid – (l)

Gaseous – (g)

Aqueous (aq)

Precipitate –(↓)

Evolution of gas- (↑)

 

Example : 3Fe_(s) + 4H₂O_(g) →Fe₂O_4(s)  + 4H_2(g)

 

Types of Chemical Reactions

   1. Combination Reaction

Two or more substances combine to form a one product.

 A+B AB

CaO + H₂O → Ca(OH)₂ + heat

   2.  Decomposition Reaction

One compound break into two or more simpler substances.

    AB → A +B

    CaCO₃  →CaO + CO₂ (Thermal decomposition)

    2H₂O →2H₂ + O₂   (Electrolysis)

     2AgCl →2Ag + Cl₂ (Photochemical decomposition)

   3. Displacement Reaction

 A more reactive metal displaces a less reactive metal.

    A + BC →AC + B

    Zn + CuSO₄ →   FeSO₄ + Cu

   4. Double displacement reaction

  Exchange of ions between two compounds.

   Ab + CD →AD+ CB

 

   Na₂SO₄ + BaCl₂ →BaSO₄↓ + 2NaCl

   5. Precipitation Reaction

Formation of an insoluble solid during the chemical reaction.

    Pb(NO₃)₂    + 2KI →PbI₂ ↓ + 2KNO₃

    6. Exothermic Reaction

  Heat is released during chemical reaction.

     CH₄  +2O₂  →CO₂ +2H₂O + heat

   7. Endothermic Reaction

 Heat is absorbed in the chemical reaction.

      

   8. Oxidation Reaction

Addition of oxygen or removal of hydrogen.

   9. Reduction Reaction

    

    Removal of oxygen or addition of hydrogen

   10.    Redox Reaction

 Oxidation and reduction reactions occur simultaneously; the reaction is called redox reaction.

    CuO + H₂ →Cu +H₂O

Copper oxide is reduced to copper metal and hydrogen is oxidized to water.

Corrosion

Slow destruction of metals due to air and moisture

Example:- Rusting of iron

    4Fe+ O₂ + xH₂O →2Fe₂O₃.xH₂O(Rust)

 

Rancidity

Spoiling of food items containing fat and oil due to oxidation and has foul smell and taste.

Prevention

i.       Airtight containers

ii.   Refrigeration

iii.  Adding antioxidants

iv. Nitrogen flushing in packets

Very important Reactions for Board Exams

    1. Mg + O₂ 2MgO

    2. Zn + H₂SO₄ ZnSO₄ + H₂

    3. Na2SO4 + BaCl2 →BaSO4↓ + 2NaCl

    4.  4Fe+ O2 + xH2O →2Fe2O3.xH2O(Rust)

    5.  Zn + CuSO4 →   FeSO4 + Cu

Key   Points to remember

i.       Always balance chemical equations

ii.    Mention physical states

iii.    Identify the type of reaction

iv.    Oxidation and reduction occur together.

v.     Corrosion and rancidity are oxidation reactions.

Conclusion

These quick revision notes on Chemical Reactions and Equations Class 10 are useful for Board Exam revision, competitive exams, concept clarity and last minute preparation.

Short Questions with Answers – Chemical Reactions and Equations

Q1. What is a chemical reaction?

Answer – A chemical reaction is a process in which one or more substance changes into new substances with new properties.

Q2. What are reactants and products?

Answer – Reactants – Substances that take part in a chemical reaction.

Products- New substance formed after the reaction.

Q3. Write two observation that indicate a chemical reaction.

Answer- (i) change in colour (ii) formation of gas

Q4. What is a balanced chemical equation?

Answer- A chemical equation in which the number of atoms of each element is equal on both sides of the equation.

Q5. Why should chemical equations be balanced?

Answer – Chemical equation should be balanced to satisfy the law of conservation of mass which states that mass is neither created nor destroyed in a chemical reaction.

Q6. What is a combination reaction?

Answer – A reaction in which two or more substances combine to form a single product.

Q7. What is a decomposition reaction?

Answer- A reaction in which one compound breaks into two or more simpler substances.

Q8. What is displacement reaction?

Answer- A reaction in which a more reactive metal displaces a less reactive metal from its compound.

Q9. What is a double displacement reaction?

Answer – A reaction in which ions are exchanged between two compounds.

Q10. What is oxidation?

Answer – Addition of oxygen or removal of hydrogen from a substance is called oxidation.

Q11.Give one example of an exothermic reaction.

Answer -  CH₄  + 2O₂  →2H₂O +heat

Q12. Give one example of endothermic reaction.

Answer – CaCO₃  →CaO +CO₂

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