Mastering Chemical Reactions and Equations: Comprehensive Class 10 Notes for Easy Revision

Mastering Chemical Reactions and Equations: Comprehensive Class 10 Notes for Easy Revision

Welcome to Triple W, your go-to source for academic guidance and learning support! In this blog post, we’re diving deep into one of the most crucial topics in Class 10 Science – Chemical Reactions and Equations. Whether you’re preparing for your upcoming exams or looking for a comprehensive revision guide, this post will help you grasp the core concepts with clarity. We’ve broken down complex reactions and equations into easy-to-understand notes, complete with examples, explanations, and tips to boost your understanding. Let’s master chemical reactions together!

• Chemical Reaction: The process in which a substance or substances undergo change, to produce new substances with new properties, is known as chemical reaction. During a chemical reaction, there is breaking of bonds between atoms of the reacting molecules to give products.
• Chemical Equation : The symbolic representation of a chemical reaction is called a Chemical Equation.

A chemical equation which simply represents the symbols and formulae of reactants and products taking part in the reaction is known as Skeletal chemical equation for reaction.

Chemical equations in which the number of atoms of different elements are same on both side are called balanced chemical equations. These equations follow law of conservation of mass.

• Symptoms of chemical change : During the chemical change there are feu observation which are generally seen.
  1. New substance will form
  2. Change in colour
  3. Change in pressure
  4. Evolution of gas, ppt formation
  5. Either heat released or absorbed
• Law of Conservation of Mass : Except nuclear reaction atoms neither could be created nor be destroyed. The total number of atoms on reactant side will be equal to total number of atoms on product side. It states that the total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants. This law is utilized to balanced chemical reactions.

Types of Chemical Reactions

All chemical reactions can be placed into one of the following categories .

1. Combustion: It involves a reaction between any combustible material and oxygen to form an oxidized product. These reactions are exothermic, meaning they produce heat. An example of this kind of reaction is the burning of napthalene:

C₁₀H₈ + 12O₂ → 10 CO₂ + 4 H₂O + heat

napthalene

1. Synthesis: A synthesis reaction occurs when two or more simple compounds combine to form another substance. These reactions come in the general form of:

A + B → AB

One example of a synthesis reaction is the combination of iron and sulphur to form iron (II) sulphide:

 

8Fe + S₈ → 8FeS

1. Decomposition: A decomposition reaction is the opposite of a synthesis reaction – a complex molecule breaks down to make simpler ones. These reactions come in the general form:

AB → A + B

One example of a decomposition reaction is the electrolysis of water to make oxygen and hydrogen gas:

2H₂O → 2 H₂ + O₂

• Single displacement : This occurs when one element replaces another element in a compound.

These reactions come in the general form of:

A + BC → AC + B

One example of a single displacement reaction is when magnesium replaces hydrogen in water to make magnesium hydroxide and hydrogen gas:

Mg + 2 H₂O → Mg(OH)₂ + H₂

1. Double displacement : This occurs when the anions and cations of two different molecules switch places, forming two entirely different compounds. These reactions are in the general form:

AB + CD → AD + CB

One example of a double displacement reaction is the reaction of lead (II) nitrate with potassium iodide to form lead (II) iodide and potassium nitrate:

Pb(NO₃)₂ + 2 KI → PbI₂ + 2KNO₃

• Acid-base: This is a special kind of double displacement reaction that takes place when an acid and a base react with each other. The H+ ion in the acid reacts with the OH– ion in the base, causing the formation of water. Generally, the product of this reaction is some ionic salt and water. Such type of reaction is also known as neutralisation reaction.

HA + BOH → H₂O + BA

One example of an acid-base reaction is the reaction of hydrobromic acid (HBr) with sodium hydroxide:

HBr + NaOH → NaBr + H₂O

Redox-Reactions : Redox reactions are those chemical reactions in which both oxidation and reduction take place simultaneously.

Oxidation

Oxidation is a process in which:

1. Oxygen is added. OR
2. Hydrogen is removed. OR
3. De-electronation either from an atom or an ion takes place.OR
4. Oxidation number of an atom increases.

      e.g.        Na  ⎯⎯→ Na⁺ + e^–

                   Cl^–  ⎯⎯→ Cl  + e^–

                   Fe⁺²  ⎯⎯→  Fe⁺³ + e^–

Reduction

Reduction is that chemical process during which:

1. oxygen is removed. OR
2. hydrogen is added. OR
3. electronation of either an atom or an ion take place. OR
4. oxidation no. of an atom decreases.

     e.g.     Cl + e⁻ ⎯⎯→ Cl⁻

               Fe³⁺ + e⁻ ⎯⎯→ Fe²⁺

Oxidising and Reducing Agent

Oxidising agent (OA)

An oxidising agent is that:

1. which undergoes reduction. OR
2. which accept electron/electrons. OR
3. whose oxidation number decreases. OR
4. oxidise others but itself gets reduced. 

e.g.,              KMnO₄, H₂SO₄, HNO₃, F₂ etc

Reducing Agent (R.A.)

A reducing agent is that atom or molecule :

1. which undergoes oxidation during reactions. OR
2. which looses electron/electrons. OR
3. whose oxidation number increases. OR
4. reduces others but itself gets oxidised

e.g.,        H₂S, FeS, Cu₂O, FeCl₂, Na, C, Fe etc.

Oxidation number

Oxidation number of an atom is either real or imaginary charge which appears to be associated with an atom, either in a molecule or an ion. In case of electrovalent molecules, the charge will be real while in case of polar covalent molecules, the charge will be imaginary. It suggests the extent of oxidation and reduction of an atom during reactions. It may be either a whole no., fraction or even zero. The positive O.N. suggests the oxidation while negative O.N. suggests reduction.

Calculation of oxidation number

1. In uncombined state or free state, the oxidation number of an element is zero. Na , P₄, F, Ca
2. In case of a molecule, the algebraic sum of the oxidation numbers of the atoms present in the molecule is equal to zero.
3. In case of ions or complex ion, the sum of the O.N. of the atoms present in the ion is equal to the charge present on the ion.
4. In combined forms :
   1. O.N. of Alkali metals is always +1. Li, Na, K, Rb, Cs are alkali metals.
   2. O.N. of alkaline earth metals is always +2 Be, Mg, Ca, Sr, Ba are alkaline earth metals.
   3. O.N. of Al is always +3.
   4. O.N. of F is always –1.
   5. O.N. of H is usually +1, in metallic hydrides of alkali metals and alkaline earth metals it is –1. In interstitial hydrides it is 0.
   6. Usually oxygen show –2 oxidation no. In peroxide its O.N. is –1. It can show positive O.N. with F. In super oxides it is –1 (eg. Pot. superoxide KO ). In ozonides it is − 1
   7. O.N. of halogens are usually –1. But in interhalogen compounds it shows +ve O.N. value. F always shows negative oxidation number value.
5. Higher O.N. of an atom of an element in a molecule or an ion can’t exceed its group no. in Mendeleev’s periodic table except Cu & Au (cupric and auric as +2 and +3 respectively, while they belong to first B group in Mendeleev’s table).
6. Alkyl groups like –CH₃ or –C₂H₅ or –alkyl are taken as +1 in oxidation number.

Balancing of Redox Equations by Oxidation Number Method

This method is based on the fact that the number of electrons gained during reduction must be equal to the number of electrons lost during oxidation. Following steps must be followed while balancing redox equations by this method.

1. Write the skeleton equation (if not given, frame it) representing the chemical change.
2. With the help of oxidation number of elements, find out which atom is undergoing oxidation/reduction, and write separate equations for the atom undergoing oxidation/reduction.
3. Add the respective electrons on the right for oxidation and on the left for reduction equation. Note that the net charge on the left and right sides should be equal.
4. Multiply the oxidation and reduction reactions by suitable integers so that total electrons lost in one reaction is equal to the total electrons gained by other reaction.
5. Transfer the coefficients of the oxidising and reducing agents and their products as determined in the above step to the concerned molecule or ion.
6. By inspection, supply the proper coefficient for the other formulae of substances not undergoing oxidation and reduction to balance the equation.

Balancing of Redox equation by Ion-Electron Method

This method involves the following steps:

1. Divide the complete equations into two half reactions:
2. One representing oxidation.
3. The other representing reduction.
4. Balance the atoms in each half reaction separately according to the following steps:
5. Balance all atoms other than oxygen and hydrogen.
6. To balance oxygen and hydrogen.
7. In Acidic Medium:
8. Add H₂O to oxygen deficient side to balance oxygen atoms.
9. Add H⁺ to hydrogen deficient side to balance H atoms.
10. In Basic Medium:
11. For each excess of oxygen, one H₂O is added and 2OH^– on the other side.
12. If H – is not balanced, then for each excess of H, one OH^– is added on the same side and one H₂O on the other side.

Corrosion

Any process of deterioration (destruction) and consequent loss of a solid metallic material through an unwanted chemical or electrochemical attack, by its environment starting at its surface is called corrosion. Corrosion always occurs at anodic areas. More active metals are corroded more easily. Corrosion is enhanced by the presence of (a) impurities, (b) air and moisture, (c) electrolytes and (d) stains in metal like dents, scratches, welding parts, etc. Corrosion of iron is called rusting. In the process of rusting, Fe metal is converted to dark brown coloured rust with formula Fe₂O₃ . xH₂O and therefore, it is in oxidation process for iron metal and oxidising agent is oxygen in presence of weak acid (H₂CO₃). Hence, rusting of iron is a redox process.

 

Prevention of corrosion

1. By coating with a suitable material (barrier protection)
2. By alloying with suitable metals e.g. Fe, Cr, V, Ni, W, etc.
3. By cathodic protection
4. By using artificial anode (Sacrificial protection) Galvanisation.

Rancidity

Rancidity is a condition produced by aerial oxidation of unsaturated fat present in foods and other products, marked by unpleasant odour or flavour. When a fatty substance is exposed to air, its unsaturated components are converted into hydroperoxides, which break down into volatile aldehydes, esters, alcohols, ketones, and hydrocarbons, some of which have disagreeable odours. Butter becomes rancid by the foregoing process and by hydrolysis, which liberates volatile and malodorous acids, particularly butyric acid. Saturated fats, such as beef tallow, are resistant to oxidation and seldom become rancid at ordinary temperatures.

 

❑❑❑

Disclaimer:

The content provided in this blog post, “Mastering Chemical Reactions and Equations: Comprehensive Class 10 Notes for Easy Revision,” is intended for educational purposes only. While we strive to ensure accuracy and clarity, we recommend students to refer to their official textbooks and consult their teachers for any specific curriculum requirements. Triple W is not responsible for any discrepancies in exam-related information or study materials. Always cross-check with your official resources for up-to-date content.