Nuclear fusion Flashcards
nuclear fusion
the joining of smaller nuclei to form larger nuclei
it releases more energy than fission but it is more difficult to obtain than through fission
e.g.
tritium and deuterium nuclei join to make a helium nuclei and release a neutron
how stars use fusion over time
fusion is the source of energy for stars
during the stable period of a stars life, vast quantities of hydrogen nuclei are converted to helium nuclei
over time heavier elements are formed and the star eventually dies
this takes billions of years
conditions/examples of fusion reactions in stars
fusion is the source of energy for stars
a typical reaction is:
[2][1]H + [3][1]H -> [4][2]He + [1][0]n + energy
the reaction takes place under very high pressure and temperature
how does fusion release energy?
the mass of the products in the reaction is slightly less than the reactants - the difference in mass is released as thermal energy
difficulties of fusion (3)
- nuclei need to get very close to each other before fusion can happen
- under normal conditions both nuclei are + charged so repel each other (electrostatic repulsion)
- the nuclei only move fast enough to overcome the electrostatic repulsion at very high temperatures and pressures
why is fusion not a suitable source for commercial power?
the very high temperatures and pressures needed are difficult to produce as they require a lot of energy
they often use more energy than they have produced
Explain the difference between nuclear fusion and nuclear fission [3]
in nuclear fusion hydrogen nuclei fuse to produce helium nuclei whereas in nuclear fission uranium-235 splits into two smaller nuclei and two or three neutrons
nuclear fusion requires very high temperatures and pressures whereas nuclear fission requires a slow-moving neutron to be absorbed
both processes release large quantities of energy
electrostatic repulsion
when two nuclei repel each other due to electrostatic forces as they are both positively charged
Describe what happens during nuclear fusion [3]
two smaller nuclei join together to form a more stable, heavier nucleus and release energy as thermal energy
Explain why there are no commercial power stations using fusion reactions [3]
fusion reactions happen only at very high temperatures and pressures, it is very difficult to produce these conditions for any length of time, and currently more energy is needed to cause a fusion reaction than is released from it
Explain how the processes of fusion and fission release energy [4]
fusion results in the joining of smaller nuclei to form a nucleus with a slightly smaller mass
the left over mass is converted to energy
fission results in the splitting of a larger nucleus to form more stable daughter nuclei of smaller mass, with the small difference in mass being converted to energy
