Glossary of Terms
- Fuel: A substance that produces heat and light energy on burning in the presence of oxygen.
- Combustion: A chemical process in which a substance burns in air (or oxygen) with the release of heat and light energy.
- Combustible Substance: A material that catches fire easily and undergoes combustion to release energy.
- Ignition Temperature: The minimum temperature at which a combustible substance catches fire.
- Inflammable Substance: A substance that catches fire easily at a low ignition temperature.
- Supporter of Combustion: A substance like oxygen that helps in the process of combustion.
- Calorific Value: The amount of heat energy produced on complete combustion of 1 kilogram of fuel, expressed in kilojoules per kilogram (kJ/kg).
- Flame: The visible, gaseous part of a fire, formed during combustion of substances that vaporize.
- Slow Combustion: Combustion that occurs at a slow rate due to insufficient supply of air.
- Rapid Combustion: Fast combustion that occurs in the presence of sufficient air, usually in gaseous fuels.
- Spontaneous Combustion: A type of combustion where a substance catches fire on its own at room temperature without any external flame.
- Explosive Combustion: Sudden and rapid combustion that occurs in a closed space, often producing an explosion with heat, light, and sound.
- Explosion: A violent burst or blast due to explosive combustion accompanied by sound.
- Carbon Monoxide (CO): A highly poisonous gas formed during incomplete combustion of carbon-containing fuels.
- Carbon Dioxide (CO₂): A gas produced during complete combustion of carbon compounds; excess CO₂ contributes to global warming.
- Soot: Unburnt carbon particles released during incomplete combustion, appearing as black smoke.
- Non-Luminous Zone: The outermost part of a flame where complete combustion takes place; it is the hottest part.
- Luminous Zone: The middle part of a flame where partial combustion takes place; appears yellow and is moderately hot.
- Innermost Zone: The part of a flame containing unburnt fuel vapors; it is the least hot.
- Fire Extinguisher: A device used to put out fires by cutting off air supply or lowering the temperature below ignition point.
- Soda-Acid Fire Extinguisher: A type of extinguisher where acid and sodium bicarbonate react to release CO₂, which suppresses fire.
- Smog: A mixture of smoke and fog, usually formed by suspended carbon particles and other pollutants; causes respiratory issues.
- Acid Rain: Rain containing acids like sulphuric acid, formed when gases like sulphur dioxide dissolve in atmospheric moisture.
- Global Warming: The gradual increase in Earth’s temperature caused by the excess of greenhouse gases like carbon dioxide.
- CNG (Compressed Natural Gas): A cleaner and eco-friendly fuel alternative to petrol and diesel, producing fewer pollutants.
- Blow Pipe: A tool used to direct the flame at a specific point, often used by goldsmiths to melt and shape metals.
- Friction: A force that generates heat when two surfaces rub against each other, often used to ignite matchsticks.
- Cowdung Cakes: A traditional biomass fuel made from dried cow dung, typically used in rural cooking fires.
- Sulphur Dioxide (SO₂): A harmful gas released during combustion of coal and diesel; causes suffocation and acid rain.
- Ash: The solid residue left after the combustion of a solid fuel.
- Control Valve: A device used to regulate the flow and combustion rate of gaseous fuels.
- Fire Brigade: Emergency service equipped to fight and control fires in case of emergencies.
- Petroleum Products: Fuels derived from crude oil like petrol, diesel, and kerosene.
- Spirit Lamp: A small heat source used in laboratories, fueled by alcohol.
- White Phosphorus: A highly inflammable substance with a low ignition temperature (around 35°C), known for spontaneous combustion.
- Red Phosphorus: A less reactive form of phosphorus used in matchstick tips to produce ignition by friction.
- Sodium Metal: A highly reactive metal that can spontaneously catch fire when exposed to air.
- Pipeline Fuel Supply: The method of delivering gaseous fuels like LPG or CNG through pipelines directly to homes or industries.
- Gold Melting Point: Gold melts at around 1064°C; the blowpipe directs the hottest part of a flame (1300°C) to melt it efficiently.
- Electric Short Circuit: A fault in electrical wiring that can cause sparks and fire; water should not be used to douse it.
Something To Know
A. Fill in the blanks.
- A good fuel should have its ignition temperature the room ___________ temperature.
Answer – above
- Burning of cowdung cakes is an example of ___________ combustion.
Answer – slow
- The ___________ zone of a candle flame, is the coldest.
Answer – innermost
- The non-luminous zone of a candle flame is the ___________ part of the flame.
Answer – hottest
- During incomplete combustion of a fuel, ___________ gas is formed.
Answer – carbon monoxide
B. State True or False for the following statements.
- Coal is an inflammable fuel.
Answer – False
(Coal is combustible but not easily inflammable like petrol or LPG.)
- The outermost part of a candle flame contains unburnt carbon particles.
Answer – False
(The outermost part is the hottest zone with complete combustion, no unburnt carbon particles.)
- The heat produced, by burning completely one kilogram of a given fuel, is known as the efficiency of that fuel.
Answer – False
(It is called the calorific value, not efficiency.)
- All solid fuels have a higher calorific value than liquid and gaseous fuels.
Answer – False
(Gaseous fuels often have higher calorific values and burn cleaner.)
- Sulphur dioxide gas, produced during combustion of fossil fuels, causes acid rain.
Answer – True
C. Tick (✓) the correct option.
- An example of a non-combustible substance is—
petrol
wood
coal
iron
Answer – iron
- A fuel starts burning only when it is heated to—
its boiling point
its melting point
its ignition temperature
a temperature double of the room temperature
Answer – its ignition temperature
- The highest temperature zone of a candle flame, is its—
yellow zone
red zone
blue zone
orange zone
Answer – blue zone
- The amount of heat produced, on complete burning of 10 kg of a given fuel, in pure oxygen, equals H kilojoule. The calorific fuel, of that fuel, would equal—
(0.1 H) kj/kg
(10 H) kj/kg
(H+10) kj/kg
(H-10) kj/kg
Answer – (0.1 H) kj/kg
- The gas produced, due to incomplete combustion of carbon fuels, is— carbon dioxide
carbon monoxide
sulphur dioxide
nitrogen dioxide
Answer – carbon monoxide
D. Answer the following questions in brief:
- Define the term ‘combustible material’? Give two examples of combustible materials.
Answer – A combustible material is a substance that can catch fire and burn in the presence of air (oxygen).
Examples: Wood and petrol.
- State the three conditions that are needed for combustion to take place.
Answer – (i) Presence of a combustible substance,
(ii) Presence of oxygen (air),
(iii) The substance must be heated to its ignition temperature.
- State the condition under which ‘slow combustion’ of a material takes place.
Answer – Slow combustion occurs when a material burns at a slow rate without producing flames, usually at room temperature.
- Define ‘calorific value of a fuel’.
Answer – The calorific value of a fuel is the amount of heat produced by the complete combustion of 1 kilogram of the fuel, measured in kilojoules per kilogram (kJ/kg).
- State any two characteristics of an ideal fuel.
Answer – (i) It should have a high calorific value.
(ii) It should burn without producing harmful gases or residues.
- Why is water not used in controlling electrical fires?
Answer – Water is a good conductor of electricity, and using it on electrical fires can cause electric shocks or short circuits.
E. Answer the following questions.
- Draw a diagram showing the different zones of candle flame. Label the zone which contains:
(a) unburnt vapours of wax.
(b) unburnt carbon particles.
Answer –
Diagram: Zones of a Candle Flame
Copy
Download
_____________________________ / \ / (3) Non-Luminous \ ← **Hottest zone (Blue)** / (Complete Combustion) \ / \ / (2) Luminous (Yellow) \ / (Partial Combustion) \ ← **Unburnt carbon particles (soot)** / \ / (1) Innermost (Dark) \ / (Unburnt wax vapours) \ ← **Unburnt vapors of wax** ============================================= Candle Wick
Labels
- Innermost Zone (Dark):
- Contains unburnt vapours of wax(coldest part).
- Middle Zone (Luminous/Yellow):
- Contains unburnt carbon particles(soot) causing yellow glow.
- Outer Zone (Non-Luminous/Blue):
- Hottest zone (complete combustion, no soot).
Key Points:
- Unburnt wax vaporsrise from the wick and burn in outer zones.
- Soot (carbon particles)in the middle zone makes the flame luminous.
- Blue zoneis where complete combustion occurs (CO₂ + H₂O formed).
- Calorific value of wood is 18,000 kj/kg. How much of wood is required to produce 360,000 kJ of heat energy?
Answer – Amount of wood required = Total heat energy / Calorific value
= 360,000 kJ ÷ 18,000 kJ/kg
= 20 kg
- Why are gaseous fuels considered better than liquid or solid fuels.
Answer – Gaseous fuels are considered better because:
They have higher calorific values.
They burn more efficiently and produce less pollution.
They can be easily transported and controlled.
- Why do we say that ’burning of fuels’ can cause ’health hazards’?
Answer – Burning of fuels releases harmful gases like carbon monoxide, sulphur dioxide, and nitrogen oxides, which can cause respiratory problems, acid rain, and other health issues.
Value Based Question
Ameeta was upset because she could not find her black pencil and her coloured pencils set for completing her painting. Her elder sister, Suneeta helped her to locate them and then guided her in colouring her painting. She then told her that we need to be careful as we often need to fulfill a number of conditions for completing our tasks. She gave her the example of the phenomenon of ‘combustion’ and told her that combustion can be started and sustained, only if three conditions are simultaneously satisfied.
- State the values displayed by Suneeta.
Answer – the values displayed by Suneeta.
Helpfulness – She helped her younger sister find the lost items.
Supportiveness – She guided her with her painting work.
Responsibility – She taught a useful science concept using a real-life example.
Awareness and Application – She applied scientific knowledge to daily life.
Communication – She effectively communicated the importance of meeting necessary conditions to achieve a task.
- State the three conditions that need to be simultaneously satisfied for starting and sustaining combustion.
Answer – Presence of a combustible material (fuel)
Presence of oxygen (air)
Heat to raise the substance to its ignition temperature
- Ask the students to think of situations/tasks which need two or more conditions for their completion.
Answer – Examples could include:
A seed growing into a plant (needs water, air, sunlight, and soil)
Making tea (needs tea leaves, water, heat, milk/sugar optionally)
Operating a smartphone (battery power, signal/network, proper software functioning)
Lighting a matchstick (friction, oxygen, dry match)
Something To Do
- Conduct a survey of houses in your locality and find their average monthly consumption of LPG/PNG.
Answer – Instructions:
Ask 5–10 families about their average LPG or PNG usage in a month.
Note the number of cylinders or the meter reading in units.
Add all values and divide by the number of houses to get the average.
Example result: Average LPG usage = 1.2 cylinders per month
Lighting a matchstick (friction, oxygen, dry match)
- Prepare a report on the precautions that should be taken while using CNG fuel, in vehicles.
Answer – Key points:
Ensure regular checking of CNG cylinders for leaks or damage.
Do not smoke or use open flames near CNG fueling stations.
Always switch off the engine during refueling.
Get the vehicle serviced regularly at authorized CNG service centers.
Use only certified CNG kits.
- ‘Wastes’ have been traditionally disposed off by burning them. ‘Waste combustors’ are used to dispose off hospital and industrial waste. Find out how these combustors work and their effects on the environment.
Answer – Summary:
Working: Waste combustors burn waste at high temperatures (up to 1000°C) in controlled environments.
Purpose: They reduce volume, kill pathogens (in medical waste), and recover energy.
Environmental Effects:
Release toxic gases (dioxins, furans)
Contribute to air pollution and greenhouse effect
Need for emission control technologies to reduce harm
- Find out about the different types of fire extinguishers. Write the type and locations of the fire extinguishers kept in your school.
Answer –
Type of Fire Extinguisher | Used For |
Water extinguisher | Paper, wood, textile (Class A fires) |
CO₂ extinguisher | Electrical fires, computer labs |
Foam extinguisher | Flammable liquids (Class B fires) |
Dry Powder extinguisher | Versatile – used for A, B, and C fires |
Wet Chemical extinguisher | Kitchen fires (cooking oils & fats) |
School Example:
CO₂ extinguishers – Computer labs, library
Water-based extinguishers – Classrooms, corridors
Dry Powder – Near the science lab or electrical panels
Short Questions with Answers
Q1. What is ignition temperature?
Ans. The minimum temperature at which a substance catches fire and starts burning is called its ignition temperature.
Q2. Name any two substances that do not support combustion.
Ans. Carbon dioxide and nitrogen do not support combustion.
Q3. Which zone of a flame is the hottest?
Ans. The blue zone (outermost zone) of a flame is the hottest.
Q4. What is spontaneous combustion?
Ans. Combustion that starts on its own without any external heating is called spontaneous combustion.
Q5. Give an example of rapid combustion.
Ans. Burning of LPG in gas stoves is an example of rapid combustion.
Q6. What type of flame is used for welding metals?
Ans. A blue flame, which is very hot and steady, is used for welding.
Q7. Name one fuel that is used in rural areas and causes indoor air pollution.
Ans. Cowdung cakes.
Q8. What is the role of oxygen in combustion?
Ans. Oxygen helps in burning and is essential for combustion.
Q9. Name any two clean fuels.
Ans. LPG and CNG.
Q10. Why is charcoal a better fuel than wood?
Ans. Because charcoal burns without smoke and has a higher calorific value than wood.
Long Questions with Answers
Q1. What are the different types of combustion? Explain with examples.
Ans. There are three types of combustion:
Rapid Combustion: A substance burns quickly with the release of heat and light. Example: LPG.
Spontaneous Combustion: Occurs without external ignition. Example: Phosphorus catching fire in air.
Explosion: Sudden release of gas and heat with sound. Example: Firecrackers.
Q2. Write a short note on the zones of a candle flame.
Ans. A candle flame has three zones:
Innermost zone: Black and least hot, contains unburnt vapours of wax.
Middle zone (yellow): Moderately hot, contains partially burnt carbon particles.
Outermost zone (blue): Hottest and cleanest, complete combustion occurs here.
Q3. What are the harmful effects of burning fossil fuels?
Ans. Burning fossil fuels produces:
Carbon dioxide, contributing to global warming.
Carbon monoxide, a poisonous gas.
Sulphur dioxide, causing acid rain.
Smoke and soot, polluting the air and affecting human health.
Q4. What precautions should be taken while storing or using fuels at home?
Ans. Store fuels in a well-ventilated place.
Keep fuels away from heat sources.
Never leave gas burners unattended.
Use fuel-efficient appliances.
Turn off LPG regulator after use.
Additional Questions – 02
Short Answer Questions (1-2 marks)
- Why does a candle flame have three zones?
Answer: Different combustion stages—innermost (unburnt wax), middle (partial combustion), outer (complete combustion).
- Why is CO dangerous during incomplete combustion?
Answer: It binds to hemoglobin, reducing oxygen transport in blood, causing suffocation.
- What is the role of oxygen in combustion?
Answer: Oxygen supports combustion by reacting with fuel to release heat/light.
- Why can’t water extinguish oil fires?
Answer: Water sinks below oil, spreading flames; CO₂ extinguishers are used instead.
- Name two fuels with high calorific values.
Answer: Natural gas (55,000 kJ/kg), Petrol (45,000 kJ/kg).
- What causes acid rain?
Answer: Burning coal/diesel releases SO₂, which forms sulfuric acid in rain.
Long Answer Questions (3-5 marks)
- Compare rapid vs. spontaneous combustion with examples.
Answer:
Type | Rapid Combustion | Spontaneous Combustion |
Rate | Fast (e.g., LPG flame) | Instantaneous (e.g., white phosphorus) |
Oxygen Need | Requires air | Occurs without external heat |
Example | Burning matchstick | Forest fires (dry leaves + heat) |
- Explain the zones of a candle flame with a diagram.
Answer: Innermost Zone: Unburnt wax vapors (dark, coolest).
Middle Zone: Yellow, luminous (partial combustion, soot).
Outer Zone: Blue, hottest (complete combustion, CO₂ + H₂O).
- Why is CNG preferred over petrol in vehicles?
Answer: Less Pollution: CNG burns cleaner (minimal CO/soot).
High Calorific Value: More energy per kg.
Non-toxic: Safer leaks (lighter than air).
- Describe how to extinguish different types of fires.
Answer: Wood/Paper: Water (cools below ignition temp).
Oil/Electric: CO₂ extinguisher (cuts oxygen, no shocks).
Metals (Mg): Sand (smothers flames).
- How does global warming link to fuel combustion?
Answer: Fossil fuels release CO₂, a greenhouse gas.
CO₂ traps heat → Rising earth temperatures → Melting glaciers/floods.
HOTS (Higher-Order Thinking) Questions
- Why does a matchstick ignite on rubbing but wood doesn’t?
Answer: Matchstick tip has red phosphorus (low ignition temp), while wood needs higher heat.
- How would you demonstrate that oxygen is needed for combustion?
Answer – Experiment:
Place a candle in a dish of water.
Cover with a glass jar.
Observation: Flame dies as oxygen depletes; water rises in jar.
- Why do goldsmiths use the outer zone of a flame?
Answer: Outer zone is hottest (1300°C), melts gold for shaping.
Value-Based Questions
- Riya uses a solar cooker instead of LPG. What value does she show?
Answer: Environmental awareness (reduces fossil fuel use and pollution).
- A factory emits black smoke. How does this harm society?
Answer: Causes respiratory diseases (asthma) and acid rain (crop damage).
Practical Activity
Test for Soot in Incomplete Combustion
Materials: Glass slide, candle.
Steps:
Hold slide over candle flame (middle zone).
Observation: Black deposit (soot) forms.
Conclusion: Incomplete combustion releases carbon particles.
Summary Table: Types of Combustion
Type | Feature | Example |
Slow | Low oxygen (smoky) | Cow dung cake |
Rapid | Fast, with flame | LPG stove |
Spontaneous | No external heat | White phosphorus |
Explosive | Sudden, with sound | Firecrackers |