Fusion reactions and Einstein's famous equation?

Question

Scientists are having difficulty controlling hydrogen fusion reactions on Earth. Yet they can control the hydrogen reactions in a fuel cell. Explain why this is so. (Hint: Referencing Einstein's famous equation in your explanation might help.)

This is for my study sheet that is for notes only. The teacher never looks at it, never grades it, and knows that it is just for me to study before tests.

So, I am having a hard time answering the questions without any help or any answers, as there are none because not a lot of kids take the time to actually complete their study sheets. Please help me. This question is one of the most important ones on the study guide.

Answer 1

The reactions in a hydrogen fuel cell are CHEMICAL reactions, whereas the reactions in a fusion reactor (and in the sun) are NUCLEAR reactions. Here's the difference:

Chemical reactions never change the nucleus of the atom, so hydrogen always remains hydrogen and carbon always stays carbon. Chemical reactions involve atoms gaining and losing electrons, but the type of element is determined only by the nucleons (protons & neutrons). Therefore, a chemical reaction will never produce a new element that wasn't there from the start.

Nuclear reactions involve the nucleus of the atom re-forming itself. Fission means the nucleus splits, creating two or more atoms, each with a smaller atomic number. For example, if helium-4, with 2 neutrons and 2 protons in its nucleus split in half to form two nuclei each with 1 proton and 1 electron (which is deuterium, the second isotope of hydrogen), you'd have 2 deuterium atoms where you once had 1 helium atom. If this happened in reverse, and 2 deuterium nuclei merged to form helium-4, it would be a fusion reaction.

To summarize:
Chemical reactions involve only electrons, and electron interactions are relatively low-energy.
Fusion (and fission) reactions involve nucleon interactions, and the forces binding the nucleus together are much stronger than the forces that bind electrons to the nucleus. Therefore, nuclear reactions can create much more energy than chemical reactions.

High energy reactions means extreme equipment is needed. Fuel cells can operate at room temperature, while fusion reactions require millions of degrees Celsius. That's where the difficulty lies.

A side note:
Line up all the elements in order of atomic number (hydrogen = 1, helium = 2, lithium = 3, beryllium = 4, etc.). All the elements with atomic number less than 26 can undergo exothermic fusion. All the elements with atomic number greater than 26 can undergo exothermic fission. Exothermic reactions can keep themselves going because they produce more energy than they consume. This is why uranium and plutonium (atomic numbers of 92 and 94) can be used as fission bomb material. You could never use hydrogen as fission material, because it require you to continuously input energy to keep the reaction going.

FYI: My screen name is a compound that was tested as a fusion bomb (hydrogen bomb) fuel.

Answer 2

The hydrogen reactions in a fuel cell are ordinary electrochemical reactions where the hydrogen atoms marry up with oxygen and form water. The hydrogen atoms remain hydrogen atoms and the oxygen stays oxygen. Only the outer orbital electrons participate in the reaction; the atomic nuclei aren't really involved in such reactions other than as carriers of electrical charge for the electrons to hold onto and orbit around.

On the other hand, in a fusion reaction, the atomic nuclei fuse together to form other kinds of nuclei. In these reactions, the hydrogen loses its identity as hydrogen and becomes part of another kind of atom, usually helium. Although these reactions release a lot of energy, it also takes a lot of energy to force the nuclei close enough to each other to react. (You get this energy back after the reaction takes place along with the energy in the fusion reaction itself.)

Answer 3

Jeese, you're so smart, you can't tell the difference between nuclear fusion and electron transfer. Wow, does this sound bogus, or what? You don't need Einstein for this.