Consider the following chemical fuels:
H₂ CH₄ LPG
petrol kerosene
These fuels burn exothermically in air - Leaving Cert Chemistry - Question 6 - 2020
Question 6
Consider the following chemical fuels:
H₂ CH₄ LPG
petrol kerosene
These fuels burn exothermically in air.
(a) Explain the underlined term.
(b) Identify a fuel f... show full transcript
Worked Solution & Example Answer:Consider the following chemical fuels:
H₂ CH₄ LPG
petrol kerosene
These fuels burn exothermically in air - Leaving Cert Chemistry - Question 6 - 2020
Step 1
Explain the underlined term.
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Answer
Exothermic reactions are processes that release heat energy, resulting in a negative change in enthalpy (ΔH). This means that the products of the reaction have lower energy than the reactants, which is often observed in combustion reactions where fuels react with oxygen.
Step 2
Identify a fuel from the list above that (i) is often used in a Bunsen burner.
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Answer
CH₄ (methane) is often used in Bunsen burners due to its clean burning properties.
Step 3
Identify a fuel from the list above that (ii) causes the least environmental impact when burned.
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Answer
LPG (liquid petroleum gas) generally causes the least environmental impact among these fuels since it produces lower carbon emissions.
Step 4
Identify a fuel from the list above that (iii) is used in jet aircraft engines and in some central-heating boilers.
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Answer
Kerosene is commonly used in jet aircraft engines and central heating systems.
Step 5
Give the systematic IUPAC name for CH₄.
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Answer
The systematic IUPAC name for CH₄ is methane.
Step 6
What is the shape of a CH₄ molecule?
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Answer
The shape of a CH₄ molecule is tetrahedral due to the four covalent bonds formed by the carbon atom with the hydrogen atoms.
Step 7
To which homologous series does CH₄ belong?
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Answer
CH₄ belongs to the alkane homologous series.
Step 8
Why are small quantities of mercaptans added to natural gas before supplying it to consumers?
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Answer
Small quantities of mercaptans are added to natural gas to impart a detectable smell, which helps in identifying gas leaks and ensuring safety.
Step 9
Copy, complete and balance the following equation for the complete combustion of CH₄ in oxygen: CH₄ + O₂ →
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Answer
The complete balanced equation for the combustion of methane is:
ightarrow CO₂ + 2H₂O$$
Step 10
Draw the expanded molecular structure of propane.
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Answer
The expanded molecular structure of propane (C₃H₈) is:
H H H
| | |
H—C—C—C—H
| | |
H H H
Step 11
Show the arrangement of all the atoms and bonds in a propane molecule.
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Answer
In propane, the arrangement of atoms and bonds can be represented as:
H H H
| | |
H—C—C—C—H
| | |
H H H
where each line represents a covalent bond between carbon (C) and hydrogen (H) atoms.
Step 12
Identify the hydrocarbon that is the second main component of LPG.
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Answer
The hydrocarbon that is the second main component of LPG is butane (C₄H₁₀).
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