Combustion and flame

Q1) Define combustion. Name a combustible substance.

Ans: A chemical process in which a substance reacts with oxygen to give off heat is called combustion.

Example: paper.

Q2) list three types of combustion

Ans: the three types of combustion are:

Rapid combustion – spontaneous combustion - explosion

Q3) What is essential for the combustion of a substance

Ans: ignition temperature and combustible substance.  

Q4) Does combustion of a substance always produce light.

Ans: yes

Q5) write the chemical reaction to describe the burning of charcoal.

Ans:

Q6) What is ignition temperature

Ans: the lowest temperature at which a substance begin to burn is its ignition temperature .

Q7) why is complete combustion less pollution.

Ans: if the supply of oxygen is adequate, the substance will burn completely. This known as complete combustion. Complete combustion do not release carbon monoxide gas .

Q8) What are biofuels

Ans: fuels obtained from living and recently dead biological materials are known as biofuels.

Q9) Differentiate between rapid and spontaneous combustion

Ans: A burning matchstick or the LPG in the kitchen burns rapidly such a combustion is known as rapid combustion.

Some substances such as phosphorus burn in air on their own, this type of combustion is known as spontaneous combustion.

Q10) List the conditions necessary for combustion

Ans: the conditions required to start the process of combustion are a combustible substance, oxygen and ignition temperature.

Q11) when does a substance catch fire?

Ans: if a substance is a combustible substance.

Q12) what are inflammable substances? Give two examples.

Ans: substances that have very low ignition points are called inflammable substances.

Petrol, kerosene, LPG and alcohol are some examples of inflammable substances.

Q13) Define calorfic value

Ans: calorfic value is the amount of heat given off on complete combustion of 1 kg of a fuel.

Q14) what is biogas?

Ans: Biogas is the fuel produced from organic waste such as cattle dung.

Q15) Explain incomplete combustion

Ans: if the supply of oxygen is inadequate, then the combustion will be incomplete.

Q16) why is it difficult to burn a wet wool?

Ans: water is not a combustible substance.

Q17) Distinguish between complete and incomplete combustion

Ans: Combustion can be complete or incomplete. If the supply of oxygen is inadequate then the combustion will be incomplete. On the other hand if the supply of oxygen is adequate, the substance will burn completely. This is known as complete combustion.

Q18) Explain how the wax candle burns.

Ans: A candle is a column of wax. In the middle of the wax column, a cotton wick is fixed. When the wick is lighted it begins to burn. The warm liquid wax gets sucked upwards in the wick and reaches the flame. This happens due to the capillary action of the wick. On reaching closer to the flame, the liquid wax gains heat and changes into wax vapour. The hot air rises upwards carries the wax vapour into the flame and the wax vapour burns. Thus a burning candle gets a continuous supply of wax vapour and the combustion of wax continues.

Q19) list four criteria for an ideal fuel.

Ans:

 -      A fuel that has high calorific value gives our more heat. It is a better fuel.

 -      The fuel should be easily stored and transported. A fuel with very low ignition point is difficult to store and transported as it catches fire easily.

 -      The fuel should have a moderate rateot combustion it should not burn too quickly.

 -      The ignition temperature of an ideal fuel should not be too high as reaching the ignition temperature will not be particular.

Q20) how has the use of CNG in automobiles reduced air pollution?

Ans: CNG is used to operate motors and it does not produce smoke. Therefore, it helps to reduce pollution.

Q21) Why can’t fire caused by liquid fuels be controlled by spraying water?

Ans: fire caused by liquid fuels such as oils, diesel and kerosene can’t be controlled by spraying water because if water is sprayed these liquids are -------- than water will float and spread and cause greater damage. It can be controlled by special materials like fire retardant, chemical dust and cooling protein foam.

Q22) write a note on biodiesel.

Ans: Biodiesel is a liquid fuel that can be made from algae. Vegetable oil and animal fats. It is biodegradable and a less polluting fuel.

The jatropha plant is a perfect biodiesel plant. The seed of this plant contain about 30 percent non edible oil which can be easily converted into biodiesel. Many state government are encouraging small farmers to grow this plant as a cash crop.

Q23) Draw a candle flame and label its different zones.

Ans: