Nuclear reactions as a source of energy
4 marks · NormalConsider the following nuclear fission equation for uranium-235:
Answer the following questions about it.
How many neutrons are produced in this fission reaction?
Verify that both mass and atomic numbers are conserved on both sides of the equation.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) 3
(b) Mass numbers: 235+1 = 236; 144+89+3×1 = 236. Atomic numbers: 92+0 = 92; 56+36+3×0 = 92. Both are conserved.
Also accept: Mass number (A) sums to 236 on both sides; atomic number (Z) sums to 92 on both sides.
Common mistakes: Forgetting extra neutrons on right side
Show mark scheme and worked solution
Marking points
A1 (a) · 1 mark · States 3 neutrons produced.
B1 (b) · 1 mark · Sums mass numbers on both sides and states they are equal.
B1 (b) · 1 mark · Sums atomic numbers (proton numbers) on both sides and states they are equal.
B1 (b) · 1 mark · Correctly refers to conservation of mass and charge (protons).
Worked solution
a) 3 neutrons are produced.
b) Mass numbers left: 235 (U) + 1 (n) = 236. Right: 144 (Ba) + 89 (Kr) + 3×1 (neutrons) = 236.
Atomic numbers left: 92 (U) + 0 (n) = 92. Right: 56 (Ba) + 36 (Kr) + 3×0 (neutrons) = 92.
Both mass and atomic number are conserved.