What chemical reactions occur in fireworks?



Click for a larger view.



       First the fireworks is made up of tightly packed with explosive powder designed to blast the firework high into the air and safely away from the viewers. In the beginning the firework is nothing more than a missile. As the first stage burns, the firework is powered by-action and reaction .When the gunpowder burns, it gives off hot exhaust gas that fires backward. The force of the exhaust gas firing backward creates an equal and opposite reaction force that sends the firework shooting forward through the air. 

       The second part of the fireworks has more loosely packed, finer explosive material. As the fuse burns upward, it sets fire to this stage too. Depending on how the stage is made and packed, it either creates the final, colourful explosion there and then or it shoots off a number of firecrackers in different directions. 

        When you see fireworks they always make symmetrical explosions. This occurs because of a law of conservation of momentum. The momentum of a firework must be the same before and after an explosion, so explosions are balance in both sides. Then there is the color of the fireworks. The colours are made by the burning of different types of metal compounds (also known as metal salts) packed inside. This will be explained later in more detail.

What are the Compositions of Fireworks?

• Black powder (consists of calium nitrate, charcoal, sulfur) 
• Fluorescent impulses Colorful effects are reached by adding barium, strontium and copper salts; for red coloring: strontiumoxalate, carbonate and nitrate, for green coloring: bariumoxalate, chlorate and nitrate. 
• Cracking effects (usually with a mixture of fine metal powder together with oxidation agents).  
• Whistling impulses (chlorate, perchlorate as well as saults of aromatic acids). The whistling noise is reaches with oscillation of the let-off.
• Additional impulses like smoke contain besides combustible parts vaporising or subliming ingredients. 

What gives fireworks their colour?

            One of the key characteristics of fireworks are the vibrant colours that are produced when they explode. Fireworks depend on the chemical characteristics of elements to produce the specific colour needed.  To create these colours, fireworks use the two main methods of colour production; incandescence with luminescence.

         Most fireworks use pyrotechnic composition to produce colours in fireworks. Pyrotechnic composition is a substance that produces heat, light, sound, gas or smoke resulting from an exothermic chemical reaction. When a specific type of metal is heated in a flame, it can produce a colour. For example: copper compounds over a flame can produce a green-blue glow. These natural chemical characteristics of elements are used to produce a specific colour. When the firework gets ignited and shot up, the reaction occurs and the colour producing chemical - which can come in different forms such as: metallic powers and metallic salts - produces the colour. 


          This is a chart that shows the colour of the firework and what typed of metallic compounds are used to make the specific colour.

Colour	Compound
Red	strontium salts, lithium salts lithium carbonate, Li2CO3 = red strontium carbonate, SrCO3 = bright red
Orange	calcium salts calcium chloride, CaCl2 calcium sulfate, CaSO4·xH2O,
Gold	incandescence of iron (with carbon), charcoal, or lampblack
Yellow	sodium compounds sodium nitrate, NaNO3 cryolite, Na3AlF6
ElectricWhite	white-hot metal, such as magnesium or aluminum barium oxide, BaO
Green	barium compounds + chlorine producer barium chloride, BaCl+ = bright green
Blue	copper compounds + chlorine producer copper acetoarsenite (Paris Green), Cu3As2O3Cu(C2H3O2)2 = blue copper (I) chloride, CuCl = turquoise blue
Purple	mixture of strontium (red) and copper (blue) compounds
Silver	burning aluminum, titanium, or magnesium powder or flakes

Video "How Its Made"

What is the use of black powder in fireworks?

          Black powder consists of a fuel and an oxidizer and sulphur, to allow for a stable reaction. Charcoal as a fuel and the saltpetre as an oxidizer. The carbon from the charcoal plus oxygen produces carbon dioxide which is energy. This reaction would be slow, like a wood fire, except for the oxidizing agent the potassium nitrate.  Since the carbon in a fire must have oxygen from the air. Saltpetre provides the extra oxygen it needs. Potassium nitrate, sulphur, and carbon react together to form nitrogen and carbon dioxide gases and potassium sulphide. These expanding gases, nitrogen and carbon dioxide, provide the propelling action of the fireworks to fly.

  

           It’s not very complicated to make black powder. Typical modern gunpowder consists of 75% potassium nitrate (KNO3), 15% charcoal (carbon), and 10% Sulphur. But these percentages change with the types of fireworks because the changing of the amounts of the ingredients affects the rate in which the black power burns and the amount of smoke that is made.

What is the cause for the duration of fireworks?

              For visual effects in fireworks pyrotechnic chemists are not trying to create an explosion, they want to burn the ingredients slowly to make a longer and brighter show. For this to occur, chemists have to use a specific size for the each of the particles of the ingredients. Also the ingredients have to be blended just right to get the right effect.

              To make the burning of the ingredients of the fireworks slower chemists use larger grains of the chemicals to about 250 to 300 microns (its the size of a small grain of sand). Then the ingredients are not mixed very well so that it makes it harder for the fuel and oxidizer to combine and burn. For the even brighter and flashy parts of the fireworks they use even larger grain that are about 1 thousand microms in size. This produces a longer and brighter effect.

How do fireworks get shoot into the air?

             Rocket fireworks have a aerial shell to shoot themselves up to the sky and explode. Modern fireworks use compressed air to shoot themselves into the air and then use an electric timer to explode. Most fireworks use gun-powder to launch up and explode. The firework function as a two stage rocket. The first stage of the fire work areal shell is a tube containing gun-power. There is a hole at the bottom of the firework so the expanding gases from the gun-powder propel the firework into the air rather than exploding. The second stage of the areal shell is a package of gun-power, oxidizers and colourants. This will determine the shape of the firework.

Work Cited

http://en.wikipedia.org/wiki/Pyrotechnic_composition


http://chemistry.about.com/od/howthingswork/a/fireworks.htm


http://chemistry.about.com/od/fireworkspyrotechnics/a/fireworkcolors.htm


http://www.youtube.com/watch?feature=player_embedded&v=88TVh1O5P1o


http://www.msnbc.msn.com/id/3077329/


http://chemistry.about.com/od/fireworkspyrotechnics/a/black-powder-composition.htm


http://upload.wikimedia.org/wikipedia/commons/7/7c/Flametest--Cu.swn.jpg


http://www.ch.ic.ac.uk/local/projects/gondhia/construction.html