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Finding Chemical Reactions and Equations Class 10 confusing at first? Don’t stress - this chapter is more logical than it seems. It mainly focuses on how substances change, how those changes are written as equations, and how to identify different types of reactions. Once you get the basics, everything starts falling into place.
From balancing chemical equations to knowing oxidation, reduction, corrosion, and rancidity, these ideas are important both for exams and real life. So if you’re looking for clear, no-extra-theory Science notes that help you revise quickly, you’re in the right spot.
Chemical Reactions and Equations Class 10 Notes
If you want Class 10 Chemical Reactions and Equations notes that are simple and exam-ready, this page is made for you. No heavy textbook language - just well-organised concepts and explanations that actually help during revision.
Whether it’s reaction types, balanced equations, or common CBSE questions from this chapter, everything is explained here in one place to save your time before tests.
Below are the free PDF notes for chemical reactions and equations.
What Is a Chemical Reaction?
A chemical reaction is a process in which one or more substances (called reactants) change to form new substances (called products). The products formed have different properties from the original substances.
How Do We Know a Reaction Has Occurred?
A chemical reaction can usually be identified by observable changes, such as:
- Change in colour
- Change in state (solid, liquid, gas)
- Release or absorption of heat
- Formation of gas
- Formation of a precipitate
- Change in energy
Daily Life Examples of Chemical Reactions
Chemical reactions are not limited to laboratories - they happen all around us. Some common examples include:
- Milk turning sour
- Rusting of iron
- Cooking food
- Respiration
- Ripening of fruits
- Fermentation
Chemical Equations – Representing Reactions Simply
A chemical equation is a short way to show a chemical reaction using symbols and formulas. Instead of writing long sentences, you can quickly see what reacts, what’s formed, and in what proportion. This makes it super handy for quick revision and solving problems.
Parts of a Chemical Equation
- Reactants: These are the starting stuff that react. Always on the left side. Think of them as the ingredients.
- Products: The new stuff that forms after the reaction. They go on the right side. These are like your finished dish.
- Arrow (→): This shows the reaction direction - basically, “reactants turn into products.” Sometimes, you’ll see extra stuff like heat & light, or a catalyst written above or below the arrow.
Types of Chemical Equations
1. Word Equation – Just spells it out in words. Easy to understand what’s happening without formulas.
Example: Magnesium + Oxygen → Magnesium oxide
2. Skeletal Equation – Uses chemical formulas instead of words but isn’t balanced yet. Shows what’s involved but not the exact number of atoms.
Example: Mg + O₂ → MgO
Chemical equations are basically your reaction cheat sheet. Once you know how to balance them, you’re obeying the law of conservation of mass - meaning no atoms disappear or magically appear.
Balanced Chemical Equations
A balanced chemical equation makes sure that the number of atoms of each element is the same on both sides of the reaction. This follows the Law of Conservation of Mass, which simply means mass can’t appear out of nowhere or disappear during a chemical reaction. Everything that goes in must come out in some form!
Steps to Balance a Chemical Equation
Here are some of the steps to balance a chemical equation:
1. Write the skeletal equation – just the formulas, unbalanced.
2. Count the atoms of each element on both sides.
3. Balance one element at a time – usually start with the element that appears in the largest number.
4. Balance free elements last – like O₂, H₂, or other elemental molecules.
5. Double-check everything – make sure the number of atoms matches on both sides.
Making Chemical Equations More Informative
A chemical equation doesn’t just show what reacts and what is formed - it can also give extra details about physical states and reaction conditions. This helps you understand how and under what conditions a reaction takes place.
Physical State Symbols
The physical state of each substance is written in brackets after its formula:
- (s) – solid
- (l) – liquid
- (g) – gas
- (aq) – aqueous (dissolved in water)
Example: 3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)
Here, H₂O(g) means water is present as steam, not liquid water.
Reaction Conditions
Sometimes a reaction needs special conditions like heat, pressure, light, or a catalyst. These conditions are written above or below the arrow (→) in the chemical equation so they are easy to notice.
Types of Chemical Reactions
Types of chemical reactions are an important topic in Class 10 Chemistry. Once you know the basic pattern of each reaction, identifying them in questions becomes much easier.
1. Combination Reaction
As the name suggests, things combine here. When two or more substances react to form a single product, it’s called a combination reaction.
General form: A + B → AB
Examples:
- CaO + H₂O → Ca(OH)₂ + Heat
- 2H₂ + O₂ → 2H₂O
2. Decomposition Reaction
This is the opposite of a combination. Here, one compound breaks down into two or more simpler substances.
General form: AB → A + B
Types:
- Thermal decomposition
- Electrolytic decomposition
- Photochemical decomposition
Example: 2AgCl → 2Ag + Cl₂ (sunlight)
3. Displacement Reaction
Think of this as a replacement. A more reactive element pushes out (displaces) a less reactive element from its compound.
Example: Fe + CuSO₄ → FeSO₄ + Cu
4. Double Displacement Reaction
Here, two compounds exchange ions with each other.
General form: AB + CD → AD + CB
Example: Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
Subtypes:
- Precipitation reaction
- Neutralisation reaction
Exothermic and Endothermic Reactions
Some chemical reactions involve a change in energy, usually in the form of heat. Based on this energy change, reactions are classified as exothermic or endothermic.
Exothermic Reactions
In an exothermic reaction, heat is released to the surroundings. This means the surroundings become warmer during the reaction.
Common examples:
- Combustion (burning of fuels)
- Respiration (release of energy from food in living organisms)
These reactions usually feel hot and release energy.
Endothermic Reactions
In an endothermic reaction, heat is absorbed from the surroundings. As a result, the surroundings may feel cooler.
Common examples:
- Decomposition reactions (breaking down compounds using heat or energy)
- Photosynthesis (plants absorb energy from sunlight)
These reactions need a continuous supply of energy to take place.
Oxidation and Reduction (Redox Reactions)
In most chemical reactions, something loses and something gains. This is where oxidation and reduction come in. These two processes always happen at the same time, which is why such reactions are called redox reactions.
When we talk in simple terms:
- Oxidation happens when a substance gains oxygen or loses hydrogen.
- Reduction happens when a substance loses oxygen or gains hydrogen.
So, if one substance is getting oxidised, another substance must be getting reduced along with it.
Now comes the role of agents:
An oxidising agent helps another substance get oxidised. While doing so, it gets reduced.
A reducing agent helps another substance get reduced, and in the process it gets oxidised.
Easy way to remember:
- Oxidising agent = gets reduced
- Reducing agent = gets oxidised
Effects of Oxidation in Daily Life
Oxidation reactions don’t just happen in labs - we see their effects around us every day. Some of these effects are harmful, while others are useful. Two important effects of oxidation you should remember for exams are corrosion and rancidity.
Corrosion
Corrosion is the slow damage of metals when they react with oxygen, moisture, or air over time. The most common example is rusting of iron, where iron reacts with oxygen and water to form rust. Corrosion weakens metals and reduces their lifespan.
To prevent corrosion, metals are protected by:
- Painting the surface
- Galvanisation (coating with zinc)
- Oiling or greasing to keep air and moisture away
Rancidity
Rancidity happens when fats and oils get oxidised, causing food to develop a bad smell and unpleasant taste. This is why chips or oil-rich foods spoil when left open for too long.
Rancidity can be prevented by:
- Storing food in airtight containers
- Keeping food in the refrigerator
- Adding antioxidants to food
- Nitrogen flushing, used in food packets to slow oxidation
FAQs
Q1. What is a chemical reaction?
Ans. A chemical reaction is a process in which one or more substances change and form new substances with different properties.
Q2. What is a balanced chemical equation?
Ans. A balanced chemical equation is one in which the number of atoms of each element is equal on both sides of the equation, showing that mass is conserved.
Q3. What is a decomposition reaction?
Ans. A decomposition reaction is a reaction in which a single compound breaks down into two or more simpler substances using heat, light, or electricity.
Q4. What is a displacement reaction?
Ans. A displacement reaction is a reaction in which a more reactive element replaces a less reactive element from its compound.
Q5. What is rancidity?
Ans. Rancidity is the process in which fats and oils in food get oxidised, resulting in a bad smell and unpleasant taste.
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