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The structure of one molecule of a compound is shown in Figure 10 - Edexcel - GCSE Chemistry - Question 7 - 2022 - Paper 1
Question 7
The structure of one molecule of a compound is shown in Figure 10. (a) What is the molecular formula of the compound in Figure 10? A CH B CH₂ C C₃H₆ D C₈H₁₈ (... show full transcript
Worked Solution & Example Answer:The structure of one molecule of a compound is shown in Figure 10 - Edexcel - GCSE Chemistry - Question 7 - 2022 - Paper 1
Step 1
Step 2
State why the compound is described as an unsaturated hydrocarbon.
Answer
The compound is described as an unsaturated hydrocarbon because it contains at least one carbon-carbon double bond (C=C). This double bond prevents the molecule from achieving the maximum number of hydrogen atoms, characteristic of saturated hydrocarbons.
Step 3
Step 4
Calculate the mass of this molecule of Y in g.
Answer
To find the mass of one molecule of substance Y, we multiply the mass of one molecule of the compound by the number of molecules:
Mass of one molecule of Y = 64,800 molecules × 6.98 x 10⁻³ g = 452.784 g.
Thus, the mass of one molecule of Y is approximately 452.78 g.
Step 5
Discuss the complete and incomplete combustion of these alkanes and the trend in the energy changes they produced.
Answer
In the complete combustion of alkanes, the reactants (alkanes and oxygen) yield carbon dioxide and water, releasing a significant amount of energy. The general equation for complete combustion can be represented as:
Alkane + O₂ → CO₂ + H₂O + Energy.
Conversely, incomplete combustion occurs when there is insufficient oxygen, leading to the formation of carbon monoxide or soot along with carbon dioxide and water. The equation for incomplete combustion is:
Alkane + O₂ → CO + H₂O + Energy (or C + H₂O + Energy).
As observed in Figure 12, the energy released increases with the number of carbon atoms in the alkanes. This trend indicates that larger alkanes, such as butane, release more energy due to the greater number of C-H bonds available for combustion. Methane, with the lowest temperature change, releases the least energy, while butane, exhibiting the highest change, releases the most.