1. Burning … is a chemical reaction: fusion with oxygen Coal:
Hydrogen (gas):
More precisely:
Octane (car fuel):
Oxygen
coming form the air
Notice: number of atoms is conserved.
(No change of nuclei in chemistry!)

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Question 12
What is burning?
A The production of heat.
B Conversion of electrical energy into heat and light.
C A chemical fusion with oxygen.
D A nuclear reaction that turns hydrogen, carbon, or other chemical elements into more complicated ones and releases heat.
E The production of energy.

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Question 13
What chemical do you need (other than the coal)
for burning coal and what is the result?
A Need: oxygen; Result: carbon dioxide.
B Need: carbon; Result: oxygen.
C Need: hydrogen; Result: water.
D Need: nitrogen; Result: nitrogen acid.
E Need: oxygen; Result: only ash.

4. (Numbers refer to the Sun) Nuclear fusion: 10 billion years
What fuels the stars?
Stars radiate a lot of energy: need to keep up for a long time - need very effective fuel
Logic:
calculate total radiated energy
divide by energy contained per kg of known fuel
get max time that fuel can maintain star
Burning wood: 20 years
Burning car fuel: 230 years
Best chemical process: 2,100 years
Radioactive decay: 10 years
Nuclear fission: 2000 years
Not nearly long enough
(atomic bomb)
(Numbers refer to the Sun)
(hydrogen bomb)
Nuclear fusion: 10 billion years
That is what it is!

5. The calculation
Stars radiate a lot of energy: need to keep up for a long time - need very effective fuel
Logic:
calculate total radiated energy
divide by energy contained per kg of known fuel
get max time that fuel can maintain star
Here is the calculation:
1: The solar constant is 1,400 W/m2; this crosses each m2 of a sphere with radius 1 AU = 1.51011 m.
2: Surface area of this sphere = 4r2 = 4  3.14  (1.51011 m)2 = 2.83 1023 m2
3: The total power radiated by the Sun is 1,400 W/m2  1023 m2 = 3.97 1026 W
4: The mass of the Sun is 1.99 1030 kg
5: The power produced per each kg is 3.97 1026 W/ 1.99 1030 kg = 2 10-4 W/kg - does not look much
6: Hydrogen burning (2H+OH2O) releases 1.33 107 W sec / kg energy per kilogram, so it could last
(1.33 107 W sec / kg) / (2 10-4 W/kg) = 6.65 1010 sec = 2,100 years

6. Nuclear processes Decay (occurs in nature) Fission (Reactors & A-bomb)
Fusion (H-bomb)
Nuclear processes
Don’t confuse with chemical processes!
They don’t change one atom into another.

7. Hydrogen to helium fusion
This reaction needs
heat > 1 million K
(only in very center of star!)
4 H  He + heat
(Call it H ‘burning’ - it is really not!)
Mass of
1 proton units
4 protons units
1 He units
Missing units = 0.8%
Becomes energy:
E = m c2

8. Questions coming …

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Question 14
What keeps the Sun shining?
A It burns hydrogen into water.
B It produces helium from hydrogen.
C It produces heavier elements from helium.
D It is hot and cooling slowly as it gives off its heat.
Next question coming …

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Question 15
Where in the Sun is there heat production?
A Everywhere.
B Only in the center.
C Nowhere. The Sun in only giving off its existing heat.
D Only on the surface.
Next question coming …

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Question 16
Which of the following uses the same physical process as the Sun to generate heat?
A A gas stove.
B A wood stove.
C A hydrogen bomb.
D An atomic bomb.
E A nuclear reactor.