Question
Both fission and fusion reactions are potential sources of nuclear energy.
(a) Compare and contrast the nuclear changes and products formed in these processes
giving one similarity and one difference.
Similarity:
Difference:
(b) Uranium is converted into a gaseous compound for enrichment.
(i) Identify the gaseous compound.
(ii) Determine the percentage difference in the rate of diffusion of molecules containing \(^{235}U\) compared to those containing \(^{238}U\). The molar masses of these molecules are 349 and 352 respectively. Use section 1 of the data booklet.
(iii) (iii) Show how the dependence of the rate of diffusion on molar mass arises from kinetic theory. Use section 1 of the data booklet and:
\(E = \frac{1}{2} mv^2\),
where E is energy of the particle, m its mass and v its velocity.
(c) Some reactors convert \(^{238}U\) into another nucleus that can also undergo fission.
(i) Complete the equation for this process by identifying the reacting particle, X, and the isotope formed, Y.
\(^{238}U + X \rightarrow ^{239}U \rightarrow Y + 2^o \beta \)
X:
Y:
(ii) The intermediate, \(^{239}U\), has a half-life of 23 minutes. Outline what is meant by half-life.
Answer/Explanation
Answer:
(a) Similarity:
increase binding energy «per nucleon»
OR
«can» produce chain reactions
Difference:
fusion forms one product/products with a greater «atomic» mass AND fission
multiple products/products with a lower mass
OR
fission produces «long lived» radioactive products/nuclear waste AND fusion
does not
(b) (i) uranium hexafluoride/\(UF_6\)
(ii) «\(^{238}U\) rate = \(^{235}U\) rate x \((349/352)^{1⁄2}\) = \(^{235}U\) rate x » 0.996
OR
«\(^{235}U\) rate = \(^{238}U\) rate x \((352/349)^{1⁄2}\) = \(^{238}U\) rate x » 1.004
percentage difference «= (1-0.996) x 100» = 0.4%
(iii) rate of diffusion proportional to v
v inversely proportional to √m
OR
v = \((2E/m)^{1⁄2}\)
OR
\(\frac{v_1}{v_2} = \frac{(2E/m_1)^{1/2}}{(2E/m_2)^{1/2}}\)
(c) (i) X: «1»n/neutron
Y: \(^{239}Pu\)/Pu – 239/plutonium-239
(ii) time for half the number of atoms/nuclei/mass to decay
Question
Geological transformations produce fossil fuels.
(a) Combustion of coal emits particulates into the atmosphere.
(i) Outline why this affects global warming.
(ii) State the major form of energy produced by the combustion of coal.
(b) Conversion of petroleum to petrol (gasoline) involves fractional distillation and cracking.
Distinguish between these processes.
Fractional distillation:
Cracking:
(c) The equation for the combustion of octane is:
\(C_6H_{18}(l) + 12 \frac{1}{2} O_2 \rightarrow 8CO_2(g) + 9H_2O(l)\)
(i) Determine the mass of carbon dioxide, in g, produced when 1kJ of energy is produced. Use section 13 of the data booklet.
(ii) Suggest a piece of evidence that leads some people to not accept a causal link between the industrial emission of greenhouse gases, such as \(CO_2\), and global warming.
Answer/Explanation
Answer:
(a) (i) reflects «sun» light
(ii) electrical/electricity
(b) Fractional distillation (Any one of):
separates compounds according to boiling points/vapor pressure
OR
physical process
OR
involves breaking intermolecular forces
OR
separates based on molar masses
OR
does not use catalyst
Cracking (Any one of):
shorter hydrocarbon chains formed/lower molar masses
OR
increased branching formed
OR
increased aromatic ring formation
OR
produces alkenes/unsaturated hydrocarbons
OR
chemical process
OR
new compounds formed/breaking «and remaking»/changing covalent bonds
OR
uses catalyst
(c) (i) ALTERNATIVE 1
5470 «kJ» produced when 8 «mol» produced
«8 x 44.01 =» 352 «g» to produce 5470 «kJ»
1 «kJ» would release «352/5470 =» 0.0644 «g»
ALTERNATIVE 2
1 «kJ»/5470«kJ=» \(1.828×10^{-4}\)
8/5470 «mol =» 0.001463 mol
«8/5470 «mol» x 44.01 «g\(mol^{-1}\) =» 0.0644 «g»
(ii) many fluctuations of temperature have occurred in the «geological» past
OR
different global models produce different outcomes
OR
industrial emissions are less than natural ones