Chapter 15 of 23

65%

Tamil Nadu (TNBSE)Class 8 Science★ 5-8 marks in the TN Class 8 annual exam through book-back MCQs, fill-ups and short answers

Chemistry in Everyday Life

Samacheer Kalvi (TN State Board) Class 8 Science — Chemistry Chapter 15, Chemistry in Everyday Life. Hydrocarbons and fossil fuels, coal and its destructive distillation (coke, coal gas, coal tar), petroleum and its refining, types of fuel and calorific value, LPG and CNG (and the mercaptan added for leak detection), and renewable energy sources. Notes with the actual book-back questions, common mistakes and quick revision.

⏱ 16 min readEasy difficulty✓ Free · NCERT-aligned

Worksheet

Podcast

Listen as a conversation

A teacher & a student talk through the chapter — in your language.

Mind Map

The chapter at a glance

Every concept and exam-favourite branch — revisable in 5 minutes.

…

Study Guide

Night-before notes

Key points, glossary and the questions most likely to show up.

…

VocabularyBuild your vocabularyLexiGenome mines the key words and schedules them with spaced repetition.Mine words →

By the end of this chapter you'll be able to…

1Define hydrocarbons and fossil fuels
2Describe destructive distillation of coal and refining of petroleum
3Define calorific value and its unit
4Expand LPG and CNG and name their key facts
5List renewable sources of energy

💡

Why this chapter matters

Chemistry in Everyday Life explains the fuels we use — coal, petroleum, LPG and CNG — how they are processed and compared by calorific value, and why we are moving to renewable energy. Mercaptan in LPG, methane in CNG and calorific value are directly tested book-back content in the TN Class 8 exam.

Before you start — revise these

A 5-minute refresher here will save you 30 minutes of confusion below.

🔗

Chapter 11 — Air

Combustion needs oxygen.

Chemistry in Everyday Life — Class 8 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 8 Science, Chemistry — Chapter 15. Fuels — from coal and petroleum to LPG, CNG and renewables.

1. About this chapter

This chapter covers hydrocarbons and fossil fuels, coal and its products, petroleum and its refining, types of fuel and calorific value, LPG and CNG, and renewable energy sources.

2. Hydrocarbons and fossil fuels

Hydrocarbons are compounds of carbon and hydrogen only; they are the main components of fuels.
Fossil fuels — coal, petroleum and natural gas — formed from the buried remains of plants and animals over millions of years. They are non-renewable (exhaustible).

3. Coal and petroleum

Coal is heated in the absence of air (destructive distillation) to give coke (pure carbon, used in steel-making), coal gas (a fuel) and coal tar.
Petroleum ("rock oil") is a mixture separated by refining (fractional distillation) into petrol, diesel, kerosene, LPG, bitumen and more.

4. Fuels and calorific value

The calorific value of a fuel is the heat released by completely burning 1 kg of it; its unit is kilojoule per kilogram (kJ/kg). A good fuel has a high calorific value, ignites easily and leaves little residue.
LPG (Liquefied Petroleum Gas) and CNG (Compressed Natural Gas) are clean fuels. The main component of natural gas (CNG) is methane.
A strong-smelling substance, ethyl mercaptan, is added to LPG to detect leakage.
Renewable (inexhaustible) sources: solar, wind and bio-energy.

5. Worked examples

Example 1. What is added to LPG to detect leakage? Ethyl mercaptan (a strong-smelling substance).

Example 2. What is the main component of natural gas? Methane.

Example 3. What is the unit of calorific value? Kilojoule per kilogram (kJ/kg).

6. Book-back questions (Samacheer Kalvi)

I. Choose the correct answer

The chemical added to LPG to detect its leakage is — (a) ethyl mercaptan / (b) methane. Ans: (a) ethyl mercaptan.
The main component of natural gas (CNG) is — (a) methane / (b) butane. Ans: (a) methane.
The unit of calorific value of a fuel is — (a) kJ/kg / (b) kg. Ans: (a) kJ/kg.
Heating coal in the absence of air is called — (a) destructive distillation / (b) refining. Ans: (a) destructive distillation.
An example of a fossil fuel is — (a) coal / (b) hydrogen. Ans: (a) coal.

II. Fill in the blanks 6. CNG stands for Compressed Natural Gas. 7. LPG stands for Liquefied Petroleum Gas. 8. The separation of petroleum into useful fractions is called refining (fractional distillation).

III. Answer briefly 9. What is calorific value? State its unit. 10. Name two renewable sources of energy.

7. Common mistakes

Mistake: Confusing destructive distillation with refining. Fix: Destructive distillation = heating coal without air; refining = fractional distillation of petroleum.
Mistake: Saying LPG smells by itself. Fix: LPG is odourless; ethyl mercaptan is added to give the warning smell.
Mistake: Calling fossil fuels renewable. Fix: Coal, petroleum and natural gas are non-renewable (exhaustible).

8. Quick revision

Chemistry Ch 15 · hydrocarbons, fuels, calorific value.
Fossil fuels = coal, petroleum, natural gas (non-renewable).
Coal → destructive distillation → coke, coal gas, coal tar.
Petroleum → refining (fractional distillation) → petrol, diesel, kerosene, LPG.
Calorific value = heat per kg (kJ/kg); good fuel = high value.
CNG = methane; ethyl mercaptan added to LPG for leak detection.
Renewable: solar, wind, bio-energy.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Hydrocarbon

compound of carbon + hydrogen

Main part of fuels.

Calorific value

heat from burning 1 kg of fuel; unit kJ/kg

Good fuel = high value.

Coal processing

destructive distillation → coke + coal gas + coal tar

Heating without air.

Gaseous fuels

CNG = methane; LPG + ethyl mercaptan (smell)

Mercaptan detects leaks.

⚠️

Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Confusing destructive distillation with refining

✓ Destructive distillation = heating coal without air; refining = fractional distillation of petroleum.

WATCH OUT

✗ Saying LPG smells by itself

✓ LPG is odourless; ethyl mercaptan is added to give the warning smell.

WATCH OUT

✗ Calling fossil fuels renewable

✓ Coal, petroleum and natural gas are non-renewable (exhaustible).

NCERT exercises (with solutions)

Every NCERT exercise from this chapter — what it covers and how many questions to expect.

Choose the correct answer

Book-back MCQs on mercaptan, methane, calorific value and fossil fuels.

Questions

Fill in the blanks

CNG/LPG expansions and refining.

Questions

Answer briefly

Calorific value, renewable sources, coal products.

Questions

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· MCQ

The chemical added to LPG to detect its leakage is ____.

▶ Show solution

ethyl mercaptan.

Q2EASY· MCQ

The main component of natural gas (CNG) is ____.

▶ Show solution

methane.

Q3EASY· MCQ

Heating coal in the absence of air is called ____.

▶ Show solution

destructive distillation.

Q4EASY· Fill in the blanks

CNG stands for ____.

▶ Show solution

Compressed Natural Gas.

Q5EASY· Answer briefly

What is calorific value? State its unit.

▶ Show solution

The amount of heat produced by completely burning 1 kg of a fuel; its unit is kilojoule per kilogram (kJ/kg).

Q6EASY· Answer briefly

Name two renewable (inexhaustible) sources of energy.

▶ Show solution

Solar energy and wind energy (also bio-energy).

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Chemistry Chapter 15 of Samacheer Kalvi Class 8 Science.
•Fossil fuels = coal, petroleum, natural gas (non-renewable).
•Coal → destructive distillation → coke, coal gas, coal tar.
•Petroleum → refining (fractional distillation) → petrol, diesel, kerosene, LPG.
•Calorific value = heat per kg (kJ/kg); good fuel = high value.
•CNG = methane; ethyl mercaptan added to LPG for leak detection.
•Renewable sources: solar, wind, bio-energy.

Tamil Nadu (TNBSE) marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Typical chapter weightage: 5-8 marks across book-back MCQ, fill-ups and short answers

Question type	Marks each	Typical count	What it tests
MCQ / Fill	1	3-5	Mercaptan, methane, calorific value, expansions
Short Answer	2-3	1-2	Calorific value, coal products, renewables
Application	2	1	Why renewable energy

Prep strategy

Learn the LPG and CNG expansions and key facts
Remember calorific value and its unit (kJ/kg)
Separate destructive distillation (coal) from refining (petroleum)
List the renewable sources

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

Cooking and transport

LPG cooks our food; CNG runs cleaner vehicles.

Industry

Coke from coal is used to extract iron in steel-making.

Clean energy

Solar, wind and bio-energy reduce dependence on fossil fuels.

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

Quote ethyl mercaptan for LPG leak detection
State CNG's main component is methane
Give calorific value with its unit (kJ/kg)
Separate destructive distillation from refining

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

Compare the calorific values of LPG, coal and wood and explain the order.
Explain why fossil fuels must be conserved and suggest alternatives.

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

TN Class 8 Annual ExamHigh

Foundation / NMMS ScienceMedium

School unit testsHigh

AI helpers for this chapter

Generate more practice on the fly, or have the chapter explained at a different level.

⚡

Generate 5 more questions

Fresh MCQs + short-answer items based on this chapter, plus answer keys.

🧠

Explain at a different level

Re-explain the chapter at the level you actually want.

📝 My notes

Saved on this device — sign in to sync · how this works

0/600

Questions students ask

The real ones — pulled from the Q&A community and tutor sessions.

LPG itself is odourless, so a small amount of ethyl mercaptan — which has a strong smell — is added so that any leak can be detected quickly by its odour.

They burn almost completely, producing very little smoke or harmful residue compared with coal or wood, so they cause less air pollution.

Practice more, ask doubts, find a tutor

Tamil Nadu (TNBSE) Class 8 mock tests

Tamil Nadu (TNBSE) Class 8 PYQs

Ask in Q&A

Science flashcards

Related chapters

Students who read Chemistry in Everyday Life usually read these next.

Measurement

Samacheer Kalvi (TN State Board) Class 8 Science — Physics Chapter 1, Measurement. The seven base (fundamental) quantities and their SI units, systems of units (FPS, CGS, MKS, SI), derived quantities, accuracy and precision, and measuring area and volume. Notes with the actual book-back questions, worked examples, common mistakes and quick revision.

Force and Pressure

Samacheer Kalvi (TN State Board) Class 8 Science — Physics Chapter 2, Force and Pressure. Force and its effects, friction (static, sliding and rolling), pressure and its unit, pressure in liquids and atmospheric pressure, Pascal's law, and the viscosity and surface tension of liquids. Notes with formulas, the actual book-back questions, common mistakes and quick revision.

Light

Samacheer Kalvi (TN State Board) Class 8 Science — Physics Chapter 3, Light. Luminous and non-luminous objects, regular and irregular reflection and the laws of reflection, multiple reflection (periscope, kaleidoscope), refraction, and the dispersion of white light (VIBGYOR). Notes with the actual book-back questions, worked examples, common mistakes and quick revision.

Heat

Samacheer Kalvi (TN State Board) Class 8 Science — Physics Chapter 4, Heat. Heat and temperature, thermometers and fixed points, specific heat capacity, the three modes of heat transfer (conduction, convection, radiation), change of state, and conductors and insulators. Notes with the actual book-back questions, worked examples, common mistakes and quick revision.