Of all kinds of energies, the heat energy is most disorganised. This is because heat energy is the reflection of speeds and collisions of the atoms. Third law of thermodynamics states that entropy of universe is always increasing. Since entropy of a system is the measure of randomness or chaos, this means all kinds of energies when used for doing useful work waste a part in the form of heat energy.
Most of the stars are made of hydrogen. It is the fuel that they burn everyday to produced light and heat. Hydrogen atoms exist in 3 forms called isotopes namely H, D and T called hydrogen, deturium and tritium. Hydrogen contains 1 proton and 1 electron and is the simplest of all atoms found in the nature. Deturium contain 1 proton and 1 neutron in the nucleus and 1 electron on the orbit. Tritium nucleus contains 1 proton and 2 neutrons and 1 orbiting electron. The abundance of deturium and tritium atoms is very low on the surface if the earth. Also the tritium atoms are radioactive.
Chemical reactions occur using only the electrons present in the outer shells through exchange. This process of combining atoms into molecules involves very small energies. Since in nature every thing tends to settle down to state of lowest energy, it means when these molecules are formed energy is liberated. We know most of the elements on the earth are found in the form of ores which are stable forms.
There are other reactions which involve changes in the nucleus. In these reactions the atom of given element transmutes altogether into another atom and tremendous amount of energy is liberated. The atoms which have very heavy nuclii are prone to disintegration. Such type of reactions are called Fission reactions.
There is yet another category of reactions in atoms combine to form bigger atoms and release of energies. Such reactions start with lighter elements most prominently Hydrogen and its isotopes. These reactions are called Fusion reactions. Fusion reactions are source of energy liberated by the stars including our own Sun.
Nucleus of atom is very compact as compared to the size of atom. Protons which reside in the nucleus along with neutrons must overcome the forces of repulsion to be confined into such a tiny space. There is a energy which is called binding energy which results from the continuous exchanges between protons and neutron through other fundamental particles.
Similarly for such atoms to fuse require that repulsion is overcome. Atoms as we know are in constant motion with spread of different speeds which follows Boltzmann distribution. As said earlier, the speeds increase as the temperature is increased. Then they collide with each with more force and a stage is reached when they overcome the repulsion and fuse into a single entity.
In the Sun’s core temperatures reach never to 15,000,000° Celsius. Hydrogen atoms are in a constant state of agitation, colliding at very great speeds. The natural electrostatic repulsion that exists between the positive charges of their nuclei is overcome, and the atoms fuse. The fusion of light hydrogen atoms (H-H) produces a heavier element, helium.
Mass and energy are the same identities. Mass can be converted into energy and we see the examples everyday in our lives. Reverse is also true and since lots of energy is condensed to turn it into mass, so lots of energy is liberated by a very small of mass. Einstein gave us a very compact beautiful equation of energy mass equivalence.
E=mc2
Since c which is speed of light and highest possible speed with a value of 300000000 meters/sec, squaring it results in enormous number. So even if mass is small, energy obtained is phenomenal. This is explained of law of conservation of mass. In any reaction, mass and energy cannot be destroyed or created. This means the mass of all the reactants should be equal to the mass of all the products.
It so happens that the final mass of products is smaller than the starting mass of the reactants. Take for example the following fusion reaction in which 1 atom of deturium combines with 1 atom of tritium to form 1 atom of Helium and 1 neutron. The reaction is written as follows.
3H1+2H1 = 4He2 + 1n0
Masses of some elements and neutron are given below in kilograms.
| particle |  |
 |
 |
 |
 |
 |
 |
| mass (x 10-27 kg) | 1.675 | 390.173 | 154.248 | 233.927 | 5.007 | 3.343 | 6.645 |
Since 10-27 kg is common to all, let’s keep it out for later use and do the arithmetic with given values.
Mass of the reactants
= (5.007 + 3.343) =8.350
Mass of products
=(6.645 + 1.675) =8.320
So the mass lost =(8.350 -8.320)= 0. 030 x 10-27 Kgs
So this loss of mass results in the creation of equivalent amout of energy. Using the formula of Einstein we get,
E =0. 030 x 10-27 x(3×108)2=0.27×10-11 joules= 17.1 MeV
This is the energy which is generated by 1 atom of deturium and 1 atom of tritium. 1 gram of this fuel will yield energy which is sufficient to heat 9.8 cubic meters of water from 0 degree Celsius to 100 degree Celsius.
Our sun produces the light and heat by burning every second 600 million tons of hydrogen into helium, releasing an enormous amount of energy. But without the benefit of gravitational forces at work in our Universe, achieving fusion on Earth has required a different approach.
At such high temperatures as are inside the sun, atoms are ionised and all the matter exists in the form of plasma or the charged ions gas. Due to enormous gravitation pull whole mass remains constrained and does not disintegrate away.
Now scientists of many countries like France, USA, Russia, India and European countries have pooled resources to create a mini sun on the earth and this project is going on in France. It is called ITER (originally an acronym of International Thermonuclear Experimental Reactor and Latin for “the way”) is an international venture. To stimulate the internal conditions existing inside the sun on the earth reactor, temperature has to be 10 times that of sun. Most crucial step is to contain the plasma because of the absence of sun like enormous gravitation force. In this reactor, the plasma will be contained in a container but will not touch the container walls. This container is very high magnetic field which will force the ions to move inside the walls without touching them.
When this project will become successful, it will open the way to provide the world with much needed energy. This energy will be non polluting and clean with no hazardous emissions like fossil fuels.