Some background information about fire, fireworks, rockets and fire extinguishers

1. Fireworks and Extinguishers
Dr. Christoph
SC 2201
facebook.com/up.chemistry
Nov. 2015

2. What will we learn ?
• How does FIRE work
• How ROCKETS work
• Colours of FIREWORK
• How Fire EXTINGUISHERS work

3. Demo
Thailand Yasothon Rocket Festival
https://www.youtube.com/watch?v=1BB7ZGRm0xI

4. Demo
• Burn tissue paper:
(a) in beaker – then close the beaker
-> what is necessary to get a fire ?
(3 things)

5. Fire Triangle

6. Demo 2
Paper impregnated with KNO3:
Burn in beaker and close it
-> why does it continue to burn ?

7. Redox Reactions
In the paper reaction, what is reducing and what is
oxidizing agent ?

8. Oxidizingagents
Electron
acceptors

9. Demo 3
Permanganate has Mn in oxidation state +7
(highest known ox.number !)
-> it wants to have electrons to reduce Mn
Mix with Glycerol ignites by itself:
(Check the ox.numbers of Mn and C on both sides )
KMnO4 + CH2(OH)-CH(OH)-CH2(OH) 
MnO2 + CO2 + H2O + K2CO3

10. Use redox reaction for rockets
For a rocket motor we need to produce a lot of
gas that expands quickly, so it can give thrust at
the outlet.
For example: Sugar + KNO3
C12H22O11 + KNO3 --->
K2CO3 + H2O + N2 + CO2

11. Demo Video
Easy KNO3_Sugar Rocket Tutorial
https://www.youtube.com/watch?v=-LI_GmG9x8M

12. Balanced equation:
5 C12H22O11 + 48 KNO3 --->
24 K2CO3 + 55 H2O + 24 N2 + 36 CO2
So from 1 mol sugar = 342 g we get:
H2O 11 mols = 200 g
N2 5 mols = 140 g
CO2 7 mols = 336 g
Total 23 mols of gas = 680 g

13. Common gases produced
At the end of a burning reaction,
molecules with high stability are
produced, mainly:
CO2 (from C)
H2O (from C-H)
N2 (from NO2)

14. The volume of 1 mol of gas can be
estimated by the ideal gas law:
R = 8.31 N m mol−1 K−1
P in Pascal:
Suppose the pressure is 1 bar (105 N/m2) and the
temperature 25 C
Calculate the volume of 1 mol of gas : 24.8 L

15. So the 23 mol gives about 570 L at r.t. but the
higher the temperature is, the more volume is
produced
Adding some heat generating material like Al
or Mg powder to the mixture will increase the
thrust.
Calculate the volume of 1 mol gas at 500 C :
64.3 L what is more than double compared to
room temperature

16. Difference to explosives
Compared to KNO3: nitroglycerine and TNT
decompose very rapidly on ignition.
Here oxidizer and fuel are in the same molecule

17. Nitrocellulose
It is easy to produce and is used in gun ammunition
-> explosives are molecules containing fuel and
oxygen in one - so only heat is necessary to ignite

18. Fireworks
The color of fireworks come from the
“Emission spectra” of metal salts

19. Flame emission
Each element produces a typical color
when heated
Na K Li Ba
See: https://www.youtube.com/watch?v=q06GmNvxaik

20. Emission Spectra
heating metal salts causes them to send light with
typical wavelengths.

21. Origin of emission lines
Electrons falling back
to their ground state
result in emission of
light

22. When an element emits a light line at 700 nm
(red), what is the energy difference in the
atom between the electron shells ?
E = h c/λ = 1239 eV nm
λ (nm)

23. FIRE EXTINGUISHERS
Dr. Chris, UP May 2015

24. Stop a fire
-> we have to remove at least one of the three
components:
WATER: cools down and covers the surface
CO2: replaces oxygen
FOAM: cools and covers from oxygen
POWDER: replaces oxygen
COMMON MISTAKE: running around when fire is
present  causes more oxygen to reach the fire !

25. Questions
What is easier to extinguish -
burning wood or burning liquid fuel ?
How to extinguish –
burning oil ?
burning body ?
How to treat burn wounds ?

26. Types of extinguishers
http://www.fire-extinguisher101.com/agents.html

27. Extinguisher Classes
http://www.fireextinguisherrecharge.net/class-b-fire-extinguisher/

28. https://www.youtube.com/watch?v=GjSoxJF3RD4
What can be used to extinguish burning oil
( and what should be avoided) ?
What can be used to extinguish electric fire
( and what should be avoided) ?
What is the advantage of CO2 extinguishers
over wet chemical and dry powder ?