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!)
sec 10 9 11 13 14 8 12 7 2 1 3 4 6 5 15 17 26 25 27 28 30 29 16 24 19 18 23 20 22 21 Question 13 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.
sec 10 9 11 13 14 8 12 7 2 1 3 4 6 5 15 17 26 25 27 28 30 29 16 24 19 18 23 20 22 21 Question 14 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.
(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!
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 = 1.51011 m. 2: Surface area of this sphere = 4r2 = 4 3.14 (1.51011 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+OH2O) 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
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.
Questions coming …
sec 10 9 11 12 15 14 13 8 7 1 2 3 5 4 6 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22 Question 15 What is the source of energy in the Sun? 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 …
sec 10 9 11 12 15 14 13 8 7 1 2 3 5 4 6 16 26 17 27 28 30 29 24 25 23 19 18 20 21 22 Question 16 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 …
sec 10 9 11 13 14 8 12 7 2 1 3 4 6 5 15 17 26 25 27 28 30 29 16 24 19 18 23 20 22 21 Question 17 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.