This question is about the reactions of alkanes - AQA - A-Level Chemistry - Question 1 - 2018 - Paper 2
Question 1
This question is about the reactions of alkanes.
Alkanes can be used as fuels.
Give an equation for the combustion of heptane (C7H16) in an excess of oxygen.
Hept... show full transcript
Worked Solution & Example Answer:This question is about the reactions of alkanes - AQA - A-Level Chemistry - Question 1 - 2018 - Paper 2
Step 1
Give an equation for the combustion of heptane (C7H16) in an excess of oxygen.
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Answer
The combustion of heptane can be represented by the following balanced equation:
C7​H16​+11O2​→7CO2​+8H2​O
Step 2
Identify a suitable catalyst for this process.
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Answer
A suitable catalyst for the catalytic cracking of hexadecane is Zeolite or aluminosilicate.
Step 3
Give one condition other than high temperature.
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The process can be performed under slight to moderate pressure, typically around 1.5 atmospheres.
Step 4
Give an equation for the catalytic cracking of one molecule of hexadecane to produce one molecule of heptane, one molecule of cyclohexane and one other product.
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Answer
The equation for the catalytic cracking of hexadecane can be expressed as:
C16​H34​→C7​H16​+C6​H12​+C3​H8​
Here, the products are one molecule of heptane, one molecule of cyclohexane (C6H12), and propane (C3H8).
Step 5
Give equations for the propagation steps in the reaction of butane to form 2-chlorobutane.
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Answer
The propagation steps for the formation of 2-chlorobutane from butane can be illustrated as:
C4​H10​+Cl⋅→C4​H9​Cl+HCl
C4​H9​⋅+Cl2​→C4​H9​Cl+Cl⋅
In these reactions, butane reacts with a chlorine radical to form 2-chlorobutane and regenerate the chlorine radical.
Step 6
Identify the radical produced from this CFC that is responsible for the depletion of ozone in the atmosphere.
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Answer
The radical produced from a chlorofluorocarbon (CFC) responsible for ozone depletion is a chlorine radical (Cl \cdot).
Step 7
Explain, with the aid of equations, why a single radical can cause the decomposition of many molecules of ozone.
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A single chlorine radical can catalyze the destruction of multiple ozone molecules through a chain reaction. For example, the reaction begins as follows:
Cl⋅+O3​→ClO⋅+O2​
Then, the chlorine monoxide radical can further react with another ozone molecule:
ClO⋅+O→Cl⋅+O2​
In this sequence, the chlorine radical (Cl \cdot) is regenerated and can continue to react with more ozone (O3), leading to the depletion of the ozone layer.
