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 balanced equation for the complete combustion of heptane is:
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 a zeolite or aluminosilicate.
Step 3
Give one condition other than high temperature.
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Answer
The reaction should occur under slight or moderate pressure.
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 can be represented as:
C16​H34​→C7​H16​+C6​H12​+C3​H8​
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 are as follows:
Formation of a radical:
C4​H10​+Cl→C4​H9∗​+HCl
Reaction of the butyl radical with chlorine:
C4​H9∗​+Cl2​→C4​H9​Cl+Cl∗
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 CFC that contributes to ozone depletion is the chlorine radical (Cl^*).
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 initiate a chain reaction for the decomposition of ozone. The process can be summarized as follows:
The chlorine radical reacts with ozone:
Cl∗+O3​→ClO∗+O2​
The chlorine monoxide radical then reacts with another ozone molecule:
ClO∗+O3​→Cl∗+2O2​
Thus, one chlorine radical can decompose many ozone molecules (O3) in a cyclic manner.
