A fuel has these enthalpies of combustion: –2057.8 kJ mol
Which of the following correctly identifies the fuel?
- Ethanol
- Propane
- Propene
- Hydrogen
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A fuel has these enthalpies of combustion: –2057.8 kJ mol
Which of the following correctly identifies the fuel?
Methanol is a liquid fuel that is often used in racing cars. The thermochemical equation for its complete combustion is
Octane is a principal constituent of petrol, which is used in many motor vehicles. The thermochemical equation for
the complete combustion of octane is
The molar mass of methanol is 32 g mol
Consider option B:
→ 1 mole of
→
→ Heat energy of 1 gram
The table gives the heat of combustion of three different alcohols at 25°C.
→ The boiling point of straight-chained alcohols increases with their chain length.
→ Therefore the boiling point of Propan-1-ol will exist between Ethanol and Butan-1-ol
A student used the apparatus shown to investigate the combustion of octan-1-ol.
The following results were obtained by the student.
Mass of water heated | = 205 g |
Initial temperature of water | = 23.7°C |
Final temperature of water | = 60.4°C |
The following data are given.
Molar enthalpy of combustion of octan-1-ol | = – 5294 kJ mol |
Molar mass of octan-1-ol | = 130.23 g kJ mol |
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a. 0.774 grams
b. Advantage of biofuel vs fossil fuel
→ Combustion of biofuels derived from plants will have a lower greenhouse impact as the carbon dioxide released during combustion will replace that used in photosynthesis, unlike fossil fuels.
Other answers could include:
→ Biofuels are biodegradable and therefore pose a much reduced environmental threat than fossil fuels which are not.
→ Biofuels are more sustainable than fossil fuels as they are produced from renewable resources.
a. Find the heat absorbed by the water ((\q\)):
b. Advantage of biofuel vs fossil fuel
→ Combustion of biofuels derived from plants will have a lower greenhouse impact as the carbon dioxide released during combustion will replace that used in photosynthesis, unlike fossil fuels.
Other answers could include:
→ Biofuels are biodegradable and therefore pose a much reduced environmental threat than fossil fuels which are not.
→ Biofuels are more sustainable than fossil fuels as they are produced from renewable resources.
Calculate the mass of methanol that must be burnt to increase the temperature of 325 g of water by 65°C, if exactly half of the heat released by this combustion is lost to the surroundings.
The heat of combustion of methanol is 726 kJ mol ¯1. (3 marks)
7.79 g
A spirit burner containing ethanol was used to heat water in a conical flask for three minutes to measure the molar heat of combustion of ethanol.
The results from the investigation are shown.
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The table shows the heat of combustion of four straight chain alkanols.
What is the mass of water that could be heated from 20°C to 45°C by the complete combustion of 1.0 g of heptan-1-ol?
The molar heat of combustion
Calculate the energy generated per kg of
Which of the equations correctly describes incomplete combustion?
→ Incomplete combustion produces carbon and/or carbon monoxide (eliminate B and C).
→ Option D is not balanced (oxygen atoms do not equate)
The following equipment was set up to measure the heat of combustion of an alkanol.
Black deposits were observed on the bottom of the conical flask and the heat of combustion measured was lower than the theoretical value.
Which of the following equations could account for these observations?
The black deposit is carbon (soot).
By Elimination:
A: Ethane is not an alkanol (eliminate A).
B: No soot is formed in this reaction (eliminate B).
C: This reaction is incorrect as no hydrogen gas is produced (eliminate C).
The following apparatus was used in an experiment to determine the molar enthalpy of combustion of ethanol.
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a.
b. Improvement to experiment accuracy (one of many possible answers):
→ The molar enthalpy of combustion measured in the experiment was not very accurate due to heat being lost to the surroundings.
→ To improve the accuracy, it would be helpful to move the spirit burner closer to the beaker to reduce heat loss.
a. | ||
b. Improvement to experiment accuracy (one of many possible answers):
→ The molar enthalpy of combustion measured in the experiment was not very accurate due to heat being lost to the surroundings.
→ To improve the accuracy, it would be helpful to move the spirit burner closer to the beaker to reduce heat loss.
Biodiesel, an alternative fuel to diesel, may be produced from vegetable oil. The chemical reaction which converts oils from biomass into biodiesel is shown.
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The energy densities of biodiesel and diesel are 38 MJ kg ¯1 and 43 MJ kg ¯1 respectively. The densities of biodiesel and diesel are 0.90 kg L¯1 and 0.83 kg L¯1 respectively.
When 60.0 L of diesel is combusted in a typical engine, 2141 MJ of energy is released.
What volume of biodiesel would be required to produce the same amount of energy? (2 marks)
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a. Ester functional group.
b.
→ Soot is produced when a fuel source undergoes incomplete combustion due to insufficient oxygen.
→ Since biodiesel already contains oxygen atoms within its structure, it would require less oxygen to undergo complete combustion compared to diesel, and is therefore less likely to produce soot.
c.
d. Advantages of bioethanol (two examples needed only):
→ Bioethanol is sustainable because it is produced from renewable resources, whereas petrol is produced from nonrenewable crude oil reserves.
→ Additionally, bioethanol is biodegradable whereas petrol isn’t. As a result, bioethanol would pose less of an environmental threat in comparison to petrol.
→ Ethanol produces less airborne particulates that are associated with lung cancer.
Disadvantages of bioethanol (two examples needed only):
→ Bioethanol requires a large amount of arable land in order to grow crops to produce bioethanol. Thus, it would lead to soil erosion and environmental pollution.
→ More energy is also required to produce bioethanol because of the requirement for labour, fertilisation, and distillation of ethanol from fermentation.
→ If fossil fuels are used as the energy source within the manufacturing process of biofuel, it will not achieve carbon neutrality and will contribute to global warming.
a. Ester functional group.
b.
→ Soot is produced when a fuel source undergoes incomplete combustion due to insufficient oxygen.
→ Since biodiesel already contains oxygen atoms within its structure, it would require less oxygen to undergo complete combustion compared to diesel, and is therefore less likely to produce soot.
c.
d. Advantages of bioethanol (two examples needed only):
→ Bioethanol is sustainable because it is produced from renewable resources, whereas petrol is produced from nonrenewable crude oil reserves.
→ Additionally, bioethanol is biodegradable whereas petrol isn’t. As a result, bioethanol would pose less of an environmental threat in comparison to petrol.
→ Ethanol produces less airborne particulates that are associated with lung cancer.
Disadvantages of bioethanol (two examples needed only):
→ Bioethanol requires a large amount of arable land in order to grow crops to produce bioethanol. Thus, it would lead to soil erosion and environmental pollution.
→ More energy is also required to produce bioethanol because of the requirement for labour, fertilisation, and distillation of ethanol from fermentation.
→ If fossil fuels are used as the energy source within the manufacturing process of biofuel, it will not achieve carbon neutrality and will contribute to global warming.
The enthalpies of combustion of four alcohols were determined in a school laboratory.
The results are shown in the table.
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a.
From interpolating the graph, the enthalpy of combustion of butan-1-ol is –2120 kJ mol ¯1.
b. Heat loss to the surroundings.
→ The school’s results are lower in magnitude than the published values because heat is lost to the surroundings, making the measured change in temperature smaller.
Other possible answers:
→ Incomplete combustion
→ Temperature change will be reduced if combustion is incomplete as less heat is released. Enthalpy of combustion will be lower as a result.
a.
From interpolating the graph, the enthalpy of combustion of butan-1-ol is –2120 kJ mol ¯1.
b. Heat loss to the surroundings.
→ The school’s results are lower in magnitude than the published values because heat is lost to the surroundings, making the measured change in temperature smaller.
Other possible answers:
→ Incomplete combustion
→ Temperature change will be reduced if combustion is incomplete as less heat is released. Enthalpy of combustion will be lower as a result.