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
Question
Gasoline (petrol), biodiesel and ethanol are fuels.
a. Calculate the energy released, in $\mathrm{kJ}$, from the complete combustion of $5.00 \mathrm{dm}^3$ of ethanol.
b. State a class of organic compounds found in gasoline.
c. Outline the advantages and disadvantages of using biodiesel instead of gasoline as fuel for a car. Exclude any discussion of cost.
d. A mixture of gasoline and ethanol is often used as a fuel. Suggest an advantage of such a mixture over the use of pure gasoline. Exclude any discussion of cost.
e(i)When combusted, all three fuels can release carbon dioxide, a greenhouse gas, as well as particulates. Contrast how carbon dioxide and particulates interact with sunlight.
e(ii)ethane is another greenhouse gas. Contrast the reasons why methane and carbon dioxide are considered significant greenhouse gases.
e(iii)suggest a wavenumber absorbed by methane gas.
e(iv)Determine the relative rate of effusion of methane $\left(M_{\mathrm{r}}=16.05\right)$ to carbon dioxide $\left(M_{\mathrm{r}}=44.01\right)$, under the same conditions of temperature and pressure. Use section 1 of the data booklet.
▶️Answer/Explanation
Markscheme
a. $« 21200 \mathrm{~kJ} \mathrm{dm}^{-3} \times 5.00 \mathrm{dm}^3=» 106000 / 1.06 \times 10^5\langle\mathrm{~kJ} 》$
b. alkane
$O R$
cycloalkane
OR
arene
Accept “alkene”.
Do not accept just “hydrocarbon”, since given in stem.
Do not accept “benzene/aromatic” for “arene”.
c. Advantages: [2 max]
renewable
uses up waste «such as used cooking oil»
lower carbon footprint/carbon neutral
higher flashpoint
produces less $\mathrm{SO}_{\mathrm{x}} / \mathrm{SO}_2$
OR
less polluting emissions
has lubricating properties
OR
preserves/increases lifespan of engine $\boldsymbol{V}$
increases the life of the catalytic converter
eliminates dependence on foreign suppliers
does not require pipelines/infrastructure «to produce»
relatively less destruction of habitat compared to obtaining petrochemicals
Accept “higher energy density” OR “biodegradable” for advantage.
Disadvantages: [2 max]
needs conversion/transesterification
takes time to produce/grow plants
takes up land
OR
deforestation
fertilizers/pesticides/phosphates/nitrates «used in production of crops» have negative environmental effects
biodiversity affected
OR
loss of habitats «due to energy crop plantations»
cannot be used at low temperatures
variable quality «in production»
high viscosity/can clog/damage engines
Accept “lower specific energy” as disadvantage.
Do not accept “lower octane number” as disadvantage”.
d. Any one:
uses up fossil fuels more slowly
lower carbon footprint/CO2 emissions
undergoes more complete combustion
produces fewer particulates
higher octane number/rating
OR
less knocking
prevents fuel injection system build up
OR
helps keep engine clean
Accept an example of a suitable advantage even if repeated from 11c.
e(i)carbon dioxide allows sunlight/short wavelength radiation to pass through AND particulates reflect/scatter/absorb sunlight
Accept “particulates reflect/scatter/absorb sunlight AND carbon dioxide does not”.
Accept ” $\mathrm{CO}_2$ absorbs IR “radiation” AND particulates reflect/scatter/absorb sunlight”.
Do not accept “traps” for “absorbs”.
e(iicarbon dioxide is highly/more abundant «in the atmosphere»
methane is more effective/potent «as a greenhouse gas»
OR
methane/better/more effective at absorbing IR «radiation»
$O R$
methane has greater greenhouse factor
OR
methane has greater global warming potential/GWP $\boldsymbol{V}$
Accept “carbon dioxide contributes more to global warming” for M1.
e(iiiąny value or range within $2850-3090 \ll \mathrm{cm}^{-1}$ »
e(iv) rate of effusion of $\frac{\mathrm{CH}_4}{\mathrm{CO}_2}=\sqrt{\frac{44.01}{16.05}}=» 1.656$