Teacher's notes and answers to questions in the book - Hodder Plus ...

WJEC GCSE Additional Science Teacher’s Notes
ii phosphorus-32
32
15
P
32
16
S
e - 0 1
iii nickel-63
iv strontium-90
63
28
90
38
Ni
Sr
63
29
90
39
Cu
Y
e - 0 1
e - 0 1
24 24
v sodium-24 - 0 11 Na 12Mg
1e
_ Nuclear fission (pages 224–27)__________________
Discussion points
1. You do the maths: 1 atom of U-235 has a mass of 3.9 × 10 –25 kg. How many atoms of U-235 are there
in 1 kg If each atom’s nucleus can emit 3.2 × 10 –11 J of heat energy, how much heat energy could 1 kg
of U-235 produce
1
number of atoms 2.6 10
-25
3.9 10
heat energy = 2.6 × 10 24 × 3.2 × 10 –11
E = 8.3 × 10 13 J
24
2. Is nuclear power from fission worth it in terms of energy 1 kg of U-235 could produce about 83 TJ
(83 × 10 12 J) of energy. By comparison, 1 kg of best coal could produce 35 MJ (35 × 10 6 J). How much
coal would you have to burn to get the same amount of energy as 1 kg of uranium-235
energy produced by 1kg of uranium
amount of coal needed
energy produced by 1kg of coal
= 2.4 × 10 6 kg (i.e. 2.4 million kg)
3. Are there any other considerations when comparing coal and uranium
For coal it is the environmental impacts of extraction and CO 2 output.
For nuclear it is the environmental impact of radioactive waste (highly radioactive for hundreds
of millions of years).
Questions
3. Use a Periodic Table or a Table of Nuclides to write nuclear equations to summarise the following
fission reactions inside a nuclear fuel rod, occurring from the fission of uranium-235 from one neutron.
The fission products are:
a xenon-140, strontium-94 and two neutrons
235 140 94 1
92 U 54Xe
38 Sr 20
b rubidium-90, caesium-144 and two neutrons
235 90 144 1
92 U 37Rb
55 Cs 20
n
n
c
lanthanum-146, bromine-87 and three neutrons.
235 146 87 1
92 U 57La
35 Br 30
n
49