Combustion and flame Worksheet-9

Combustion and flame Worksheet-9

 

  1. Explain how water extinguishes the fire.

 

  1. Red buckets containing sand are kept in offices and cinema halls. Why?

 

  1. (a) What is a fuel?

(b) Define calorific value of a fuel.

 

  1. Give reasons.

(a) Water is not used to control fires involving electrical equipment.

(b) LPG is a better domestic fuel than wood.

(c) Paper by itself catches fire easily whereas a piece of paper wrapped around an aluminium pipe does not.

 

  1. In an experiment 4.5 kg of a fuel was completely burnt. The heat produced was measured to be 180,000 kJ. Calculate the calorific value of the fuel.

 

  1. Compare LPG and wood as fuels.

 

  1. Why is wood used as a fuel in villages? What are the disadvantages of using wood as a fuel?

 

  1.  (a) From the following fuels which fuel you will prefer to use at home and which in vehicles. Give reasons in support of your answer. – LPG, CNG, Petrol, Kerosene.

 

Answer:

  1. Water evaporates taking away heat from the fire, which in turn cools down the burning material below its ignition temperature. Use of water in some cases (liquid fire/ electrical fire) can be dangerous.

 

  1. Fires in cinema halls and offices may be due to electric faults. This type of fire can be extinguished by putting off the main power switch and throwing sand over the fire. It reduces oxygen supply to the burning substance thus extinguishing the fire.

 

  1. (a). Fuels are combustible substances of organic origin or artificially obtained substances, which are used for producing heat and energy. Wood, diesel, coal, domestic gas, petrol and biogas are some of the examples of fuels.

(b). Calorific value of a fuel is defined as the amount of heat produced in kilojoules when one gram of a fuel is completely burned.

The unit for representing calorific value is kilojoule (KJ). Calorific value is expressed in KJ/g.

The higher is the calorific value of a fuel the better is the fuel. Ex- LPG calorific value 50 KJ/g

 

  1. (a). Water should not be used over electrical fires, as it conducts electricity and can pose danger to people trying to extinguish the fire.

(b). Burning of wood produces carbon monoxide which is a poisonous gas and carbon particles which is released as soot. Whereas LPG does not produce carbon monoxide.

(c). Aluminium is a good conductor of heat.Heat from paper is conducted to aluminium thus decreasing the temperature of paper below its ignition temperature.

 

  1. The calorific value of fuel is amount of heat produced in KJ on burning 1g of fuel. The calorific value of the given fuel is 40 KJ/g

 

  1.  

 

  1. Wood is used as fuel in villages because it is readily available and cheap also.

Burning of wood produces carbon monoxide which is a poisonous gas and carbon particles are produced as soot. This can lead to respiratory diseases. Its calorific value is also low. So it should not be used.

 

  1. LPG is used as domestic fuel because of its high calorific value and it also does not produce polluting gases.

CNG is used in automobiles and is also called as clean and green fuel.

Petrol is used in automobiles and also as fuel in many industries. It produces carbon dioxide which is a greenhouse gas.

Kerosene is used as domestic fuel.