HEAT SOURCES AND FLAMES

Introduction                                  

A large number of chemical reactions use heat as one of a factor of altering the rate of reactions. Heat increases the rate or the speed of a chemical reaction.

What is heat?

This is a form of energy.

NB: Energy is the ability of doing work.

What are the sources of heat in the laboratory?

The following are the sources of heat in the laboratory:

1. Bunsen burner

2. Spirit burner

3. Gas stove

4. Electric heater

5. Kerosene stove

6. Charcoal burner

What are the burners?

     These are the sources of heat in the laboratory. All burners use fuel or electricity.

Heat may be from natural fuel such as charcoal, coal, gas, spirit (ethanol) or electricity.When fuels burn they produce heat and light.

What are the common burners used in our laboratory?

1. Bunsen burner

2. Spirit burner

3. Gas stove

 THE BUNSEN BURNER

Most experiments carried out in chemistry require some heating. It is therefore very important to have good heating tools. The common heating apparatus used in laboratory is a Bunsen burner. It is originated by the name of the owner Robert Bunsen 1885.

                                DIAGRAM OF A BUNSEN BURNER

PARTS OF THE BUNSEN BURNER

There are six main parts of the Bunsen burner and those are:

1. Base

2. Gas hole

3. Pipe point jet

4. Air holes

5. Collar/ metalring

6. Chimney (barrel)

Base-
  
Supports the burner .It makes the burner stable due to its heavy weight when placed on bench.

Gas hole/gas on-let tube,

                   lets the gas on from the gas supply.

 

Pipe point jet/jet

             Directs the gas to the barrel / chimney.

Collar

       Regulates the amount  of air entering the burner . It has air holes that can be turned open or closed depending on the kind  of a flame and hence amount of heat required.

Air holes

      These are holes on the collar which allows air to enter the burner.

Chimney 

        is a part of the burner where air from outside and gas from gas supply mix up and burn.

      HOW TO LIGHT A BUNSEN BURNER

 1. Connect the Bunsen burner by a rubber tube to the  gas supply.

 2.Close the air holes.

 3.Turn the  gas tap on to  let in sufficient gas.

 4.Quickly bring a flame at the top of the barrel.

 5.Turn the collar to adjust the air holes until you get a type of a flame you want.

 6.Adjust the gas tap until the gas supply enough to produce a non luminous flame.

 
    NOTE; To put off the flame of the burner after you finish heating a substance turn the gas tap off in order to cut off the gas supply  to the burner.

THE FLAME

What is a flame?

This is a burning gas  that gives out heat and light.  The flame is formed when fuel burns to give out heat and light.

There are the two types of Bunsen burner flames:

1. Luminous flame

2. Non-luminous flame

1. THE LUMINOUS FLAME

       Is a flame which gives out bright-yellow light. It is formed when the air holes are closed.

Characteristics of a luminous flame

• It is bright-yellow in colour

• It burns quietly.

• It has four zones.

• It is smoky and it forms soot on the apparatus or equipment

• It is unstable in other words its shape changes.

• It is hot.

The structure of a luminous flame

  Uses

Luminous flame is used for lighting purposes, but can not be used for reading because it is unstable.

NB: luminous light is due to the presence of the glowing soot particles in the flame.

2. NON LUMINOUS FLAME

        It is a flame which does not give much light. It is formed when air holes are opened.

Characteristics of non luminous flame

• It is blue in colour.

• It is noisy.

• It has three zones.

• It does not form soot.

• It is steady.

• It is very hot.

Structure of a non luminous flame

 

                USES OF NON-LUMINOUS FLAME

1. Used for heating purpose in laboratory.

2. Used in welding.

3. Used at home for cooking.

4. Used in the flame test.

•Non-luminous flame is used for heating in a chemistry laboratory and welding purposes because it is very hot and does not give out soot.

 Other examples of luminous flames are:

1. Coal gas flame

2. Kerosene lamp flame

3. Fire wood flame

4. Candle flame

Other examples of non luminous flame are:

1. Kerosene store flame

2. Gas cooker flame

3. Oxy-acetylene flame

4. Bunsen burner

STRIKING BACK (BURNING BACK)

When a Bunsen burner is burning to form a non luminous flame and a gas tap is turned off slowly. The supply of the gas is reducing in the gas air mixture. The mixture contains very little gas and much air such as mixture burns rapidly forming an explosion. In this case the flame will be accompanied by a pop sound. This is called burning back, at this time the rate of burning the gas is greater than the rate at which the gas rises up the chimney.

                DIFFERENCE BETWEEN A LUMINOUS FLAME AND A NON LUMINOUS FLAME

NON-LUMINOUS FLAME	LUMINOUS FLAME
Formed when air holes are open	Formed when air holes are closed
Comprises of three zones	Comprises of four zones
Very noisy	Silent or clam
Forms no smoke or soot on apparatus	Forms a lot of smoke or soot on apparatus
Blue and almost invisible	Bright yellow and clearly visible
Very hot flame	Not hot flame
Not bright	Very bright

Triangular flame	Wave like flame

           USES OF  DIFFERENT TYPES OF FLAMES  
* For heating purpose ,most heating in the laboratory done using an Bunsen burner .

*Is used in the flame test of certain chemical substance .

*It is suitable for welding purposes.

* Suitable for cooking.


          REVIEW  QUESTIONS

  1. a/ Define the following terms;

                               (i)Heat

                               (ii)Flame


      b/ Explain how Bunsen burner work ?

  2. a/ Mention the types of flame.

                        (i).......................

                        (ii)......................

      b/ Give the proposes of each types of a flame above.

      c/ Give the difference between the types of flame above.

  3. Mention the uses of different types of flame.

  4. Draw and label ;

              (i) A Bunsen burner

              (ii) A non luminous

              (iii) A luminous