Nuclear physics questions - GCSE Additional Science (AQA) level?

Question

Hi. Stuck on homework. Have searched for about an hour for answers. Have missed a few physics lessons due to illness.

I'm doing work on nuclear fission. the first question is:

"Once the fission process has been started, it continues by itself. Explain why."

I understand that is a chain reaction.

and the second question is:

"Many thousands of times more energy is released from 1g of nuclear fuel than from burning 1g of fossil fuel. Explain, in as much detail, why this is so."

I know that nuclear fission is an exothermic reaction.

Thank you. Very much appreciated.

Answer 1

1. This is possible because certain substances called nuclear fuels undergo fission when struck by free neutrons and in turn generate neutrons when they break apart. This makes possible a self-sustaining chain reaction that releases energy at a controlled rate in a nuclear reactor.

Answer 2

dont have a clue, and i am doint the exact same course.

i guess you are slightly ahead.

Answer 3

First Q

I remember some physicist illustrating the chain reaction during fission and how unless moderated with neutron absorption could cause an explosion.

He filled a large hall with "cocked" mousetraps each with two ping pong balls on them. then threw a single ping pong ball in the middle and filmed it from above. It was spectacular starting slowly but very quickly balls flying everywhere and soon all over.

Each nucleus gives off two neutrons so unless slowed down by neutron absorbers (wiki it) would explode.

Q2. the nuclear reaction is six orders of magnitude greater than an exothermic chemical reaction in other words a million times the energy is given off, This is because the forces in nuclear fission are greater than electromagnetic forces in chemical bonding

Answer 4

1.  The reaction is self-sustaining because each fissioning nucleus releases several neutrons which cause other nuclei to fission, so causing a chain reaction.

2. The energy released in burning chemical fuel is given by the difference between the energies of the bonds that are broken in the reactants and the energies of the bonds that are formed in the products.  Fossil fuels contain a number of relatively weak C-C, C-H and C-O bonds, which require far less energy to break than is produced in forming the much stronger C=O and O-H bonds of the CO2 and H2O products of most clean burning processes.

In a nuclear fissioning process, the energy that is gained is due to the differences in nuclear binding energy per nucleon of the initial nuclei and the product nuclei.  The most stable nucleus is Nickel-62.  Anything lighter or heavier will release energy on fusing together or fissioning until it becomes nickel, however the energy barriers to doing so are normally immense (an initial input of a vast amount of energy is required).  The reason so much more energy is involved in this process than in chemical processes is that the force which governs nuclear processes, the strong nuclear force, is much, much stronger (over very short distances) than the electromagnetic force, which governs chemical processes.