Chapter 1: Chemical Reactions and Equations

Before we jump to the chapter’s notes let’s understand few important key terms so that we can easily understand the notes

KEY TERMS

Matter :- Matter can be defined as anything which fulfils following 2 conditions

It occupies space
has mass.

It’s the “stuff” that makes up everything around us, like air, water, and even your own body. In simple terms, if you can touch it, see it, or measure it, it’s matter.

Changes in matter

Any matter around us May go through following 2 changes

Physical changes ( solid, liquid, gas) basically change In Matter’s shape, state or any changes which do not alter its chemical characteristics
Chemical changes . Chemical changes in matter occur when a substance turns into a completely different substance with new properties. It’s like a transformation where the original material is altered at a fundamental level

Chemicals:- are specific types of matter that have defined compositions and properties. They can be elements (like gold or oxygen) or compounds (like water or table salt).

NOTE ( Matter and chemicals are not the same, though they are related )

Elements:- Elements are basic building blocks of matter. They are pure substances that can’t be broken down into simpler substances by chemical means. g. Gold, Silver, carbon, oxygen etc.

“Think of a matter made up of same type of Atoms this matter can be termed as elements”

Compound :- A compound is a substance made up of two or more than two elements that are chemically combined. E.g. water (H₂O) which is made up of 2 elements Hydrogen and oxygen , and they can’t be separated from each other by physical method ( e.g. Filtration, Distillation etc)

To separate a compound, you need to start a chemical reaction that requires energy

Equation :- An equation is a mathematical statement that shows two things are equal to each other it has two sides, Usually separated by an equal sign (=) all those equation which has two sides separated by equal sign but not equal are termed as unbalanced equation
Reactants :- it can be any substance which participate in a chemical reaction
Precipitate:- there are few examples where two liquid solution have been mixed and seen a phenomenon there are few solid particles have been formed and they are not dissolving in the Liquid and settle down at the bottom these particles are termed as Precipitate in the science. They are also called insoluble salts

Notes

Let’s discuss the title of the chapter first

“Chemical Reactions and Equation”

Chemical reaction :- when two or more substances (elements or compounds) combine to create new substances with different properties is termed as chemical reaction

Chemical equation :- A chemical equation is a symbolic way to show a chemical reaction. It uses symbols, formulas, and states to represent the substances involved and what happens during the reaction. It show following things

Chemicals (reactants) involved in the reaction
Quantity of the Chemicals (Reactants)
State of the Chemicals (Reactants)
Product formed ( including it’s state quantity )

E.g. NaHCO3(s)+C6H8O7(aq) → Na3C6H5O7(aq)+H2O(l)+CO2(g)

NaHCO₃: Baking soda (solid)
C₆H₈O₇: Citric acid from lemon juice (aqueous)
Na₃C₆H₅O₇: Sodium citrate (aqueous)
H₂O: Water (liquid)
CO₂: Carbon dioxide (gas)

Chemical equation are of 2 types

Balanced chemical equation Unbalanced chemical equation

Balanced chemical equation:- Chemical equations which follow law of “Conservation of mass” I.e. total numbers of atoms in the reactant side is equals to total number of atoms the product side in short MASS OF LHS SIDE = MASS OF RHS SIDE

Unbalanced chemical equation:- Chemical equations do which follow law of “Conservation of mass” I.e. MASS OF LHS SIDE ≠ MASS OF RHS SIDE

Hence they required to be balanced

Steps to balance a chemical equation:

Write the unbalanced equation.
Count the atoms of elements on both sides.
Use coefficients to balance the number of atoms.
Ensure that coefficients are in the lowest ratio.

We will discuss about the topic in the latter part of the notes in depth

We have discussed the title in depth Now let’s understand about the signs which shows chemical reaction has been taken place and the types of chemical reaction

Signs of a Chemical Reaction

If we observe a reactant undergoing any of the following changes in the presence of other reactant(s), we can conclude that a chemical reaction has taken place:

Change in colour
Change in temperature
Formation of a gas
Formation of a precipitate
Change in state (solid, liquid, gas)

These signs indicate that new substances are being formed, confirming a chemical reaction

Types of chemical reaction

Combination Reaction

Definition: All chemical reactions in which two or more substances combine together to form a single product are called combination reactions.

Reactant1 + Reactant2 +…………. → Product (only one product)

Example: When you burn a piece of magnesium ribbon in the air, it combines with oxygen to form magnesium oxide (white ash).
Equation: 2Mg(s)+O2(g)→2MgO(s)

Daily Life Example: Lighting a matchstick. The chemicals in the match combine with oxygen to produce heat and light.

Decomposition Reaction

Definition: When A single substance breaks down into two or more simpler substances due to heat , electricity, light or any catalyst are termed as Decomposition reaction

E.g. R1 → P1 + P2

(R1 – Reactant 1. P1 – Product1 , P2 – Product 2)

Daily life example: Heating baking soda to release carbon dioxide, which makes cakes rise.

Example:- NaHCO3→Na2CO3+H2O+CO2

Types of Decomposition Reactions

1. Thermal Decomposition

Definition: Decomposition caused by heat.
Equation: CaCO₃(s) → CaO(s) + CO₂(g)
Example: Heating calcium carbonate (limestone) to produce calcium oxide (lime) and carbon dioxide.

Electrolytic Decomposition

Definition: Decomposition caused by an electric current.
Equation: 2NaCl(aq) → 2Na(l) + Cl₂(g)
Colour of Product: Sodium metal is silvery-white; chlorine gas is yellowish-green.
Example: Electrolysis of sodium chloride (saltwater) to produce sodium metal and chlorine gas.

Photodecomposition

Definition: Decomposition caused by light.
Equation: 2AgCl(s) → 2Ag(s) + Cl₂(g)
Colour of Product: Silver metal is silvery-white; chlorine gas is yellowish-green.
Example: Exposure of silver chloride to sunlight, which causes it to decompose into silver metal and chlorine gas. This reaction is used in photography.

Catalytic Decomposition

Definition: Decomposition catalysed by a catalyst.
Equation: 2H₂O₂(aq) → 2H₂O(l) + O₂(g)
Colour of Product: Hydrogen peroxide is colourless; water is colourless; oxygen gas is colourless.
Example: Decomposition of hydrogen peroxide using a catalyst like manganese dioxide. This reaction is used as a disinfectant.

Displacement Reaction

Definition: A more reactive element displaces a less reactive element from its compound. Take copper sulphate solution put iron nail in it you will see
Equation: Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)
Example: Rusting of iron nails in water (iron + copper sulfate → iron sulfate + copper). This reaction is a common example of corrosion, which can damage metal structures.

Double Displacement Reaction

Definition: The ions of two different compounds exchange places to form two new compounds.
Equation: NaCl(aq) + AgNO₃(aq) → NaNO₃(aq) + AgCl(s)
Example: Formation of a precipitate when silver nitrate is added to a solution of sodium chloride. This reaction is used in the silver halide photography process.

Neutralisation Reaction

Definition: When we mix acid and base they try to neutralise the effect of each other that’s why it is known as neutralisation reaction. We can say reaction b/w acid and base is known as neutralisation reaction
Equation: HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)
Example: Adding antacid tablets (containing bases) to neutralize stomach acid (which is acidic). This reaction is used to treat heartburn and indigestion.

Oxidation and Reduction reaction

Oxidation is a chemical process where a substance loses electrons. Imagine electrons as tiny, negatively charged balls. When a substance loses these balls, it becomes more positively charged. A Simple Example: Rusting

Features of oxidation

Addition of oxygen
Or reduction of Hydrogen

What happens: When an iron nail is left outside, it rusts. Rust is a reddish-brown substance that forms on the surface of the iron.
Why it happens: The iron in the nail loses electrons to oxygen in the air. This loss of electrons is called oxidation.
Equation: 4Fe(s) + 3O₂(g) → 2Fe₂O₃(s)
- In this equation, iron (Fe) loses electrons to oxygen (O₂) to form iron oxide (Fe₂O₃), also known as rust.

Other Examples of Oxidation:

Burning: When you burn wood or paper, the carbon in the wood or paper loses electrons to oxygen in the air, producing carbon dioxide and heat.
- Equation: C(s) + O₂(g) → CO₂(g)
Cooking: When you grill a steak, the meat is oxidized, giving it a brown colour and a cooked flavour.
- Equation: C₆H₁₂O₆(s) + 6O₂(g) → 6CO₂(g) + 6H₂O(l)
Respiration: When you breathe, your body oxidizes glucose to produce energy.
- Equation: C₆H₁₂O₆(s) + 6O₂(g) → 6CO₂(g) + 6H₂O(l)

Note: In many oxidation reactions, oxygen is involved, as it is a common oxidizing agent. However, oxidation can also occur with other substances that can accept electrons.

Reduction reaction

Reduction is a chemical process where a substance gains electrons. Remember those tiny, negatively charged balls we talked about earlier? When a substance gains these balls, it becomes more negatively charged.

Features of Reduction reaction

Addition of hydrogen or
Reduction of oxygen

A Simple Example: Electroplating

What happens: In electroplating, a metal object is coated with a thin layer of another metal. For example, you can electroplate a silver spoon with gold.
Why it happens: Gold ions (Au⁺) in the solution gain electrons from the silver spoon, becoming gold atoms and coating the spoon’s surface. This gain of electrons is called reduction.
Equation: Au⁺(aq) + e⁻ → Au(s)

Other Examples of Reduction:

Photosynthesis: Plants use sunlight to reduce carbon dioxide into glucose, storing energy.
Metallurgy: Metals are extracted from their ores through reduction processes.
Battery Charging: When you charge a battery, the positive electrode gains electrons.

Remember: Oxidation and reduction always occur together in a chemical reaction. If one substance is oxidized (loses electrons), another must be reduced (gains electrons). This is why these reactions are often called redox reactions.

Exothermic Reactions

Definition: These are chemical reactions that release energy, usually in the form of heat, to their surroundings. You can think of it as the reaction “giving off” heat.

Daily Life Example: Burning wood in a fireplace. When wood burns, it releases heat, making the surroundings warmer.

Chemical Equation:

Endothermic Reactions

Definition: These are chemical reactions that absorb energy from their surroundings. This means they take in heat, making the surroundings cooler.

Daily Life Example: Melting ice. When ice melts, it absorbs heat from its surroundings, which is why it feels cold.

Chemical Equation:

Rancidity: The Spoiling of Fats and Oils

Rancidity can be defined as a chemical reaction that occurs often with food items that contain fats or oil, fats and oil can easily react with oxygen, causing unpleasant taste and smell, this degradation is typically caused by oxidation, a chemical reaction that involves the combination of a substance with oxygen.

A Daily Life Example: Stale Chips

Have you ever opened a bag of potato chips and noticed that they taste “off”? This is often due to rancidity. The oils in the chips are exposed to oxygen in the air, which can cause them to oxidize and become rancid. This oxidation process creates compounds that have a disagreeable odour and taste, you should refrain of buying opened oily products

The Chemical Equation

While the exact chemical reactions involved in rancidity can vary depending on the specific fats and oils, a simplified representation can be given:

Fats or Oils + Oxygen → Rancid Products

Antioxidants to Prevent Rancidity

Antioxidants are substances that can prevent or delay the oxidation of other molecules. They help to neutralize harmful free radicals

Here are a few examples of antioxidants used to prevent rancidity:

Butylated Hydroxy anisole (BHA): A synthetic antioxidant commonly used in food products to prevent rancidity.

Butylated Hydroxytoluene (BHT): Another synthetic antioxidant often used in food preservation.

Vitamin E: A natural antioxidant found in various foods, including nuts, seeds, and vegetable oils.

Tocopherols: A group of compounds that includes vitamin E, which are natural antioxidants.

By adding these antioxidants to food products, manufacturers can help to slow down the oxidation process and extend the shelf life of the food

Nitrogen is the gas most commonly filled in chips packets.

Here’s why: Preservation: Nitrogen is an inert gas, meaning it doesn’t react with other substances. This prevents the chips from coming into contact with oxygen, which can cause them to become rancid or stale.

Packaging integrity: Nitrogen helps maintain the shape and texture of the chips. By filling the packet with nitrogen, there’s less air space, which reduces the likelihood of the chips being crushed or broken during transportation or storage.

Safety: Nitrogen is considered safe for consumption. It’s a natural component of the atmosphere, and in small quantities, it’s harmless.

While other gases like carbon dioxide or helium might be used in some cases, nitrogen is the most common and effective choice for preserving chips.

Colour of important compound

(important compound colour)

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