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3.1 Define the term vapour pressure - NSC Technical Sciences - Question 3 - 2020 - Paper 2
Question 3
3.1 Define the term vapour pressure. 3.2 Use the table above to answer questions that follow. 3.2.1 Describe the trend in the vapour pressure of the compounds abov... show full transcript
Worked Solution & Example Answer:3.1 Define the term vapour pressure - NSC Technical Sciences - Question 3 - 2020 - Paper 2
Step 1
Step 2
Describe the trend in the vapour pressure of the compounds above.
Answer
The vapour pressure decreases with an increase in the molar mass or chain length among the compounds, as observed from the values provided. Specifically, the vapour pressure decreases from 1-propanol (21.0 x 10² Pa) to 1-pentanol (2.2 x 10² Pa).
Step 3
Explain the answer to QUESTION 3.2.1.
Answer
In 1-pentanol, the chain length and molar mass are higher compared to 1-propanol, leading to stronger intermolecular forces due to increased London dispersion forces. More energy is required to overcome these strong intermolecular forces in 1-pentanol than in 1-propanol.
Step 4
Step 5
Explain the difference in the boiling points of the two homologous series represented by graphs A and B.
Answer
Aldehydes exhibit higher boiling points due to the presence of stronger dipole-dipole forces, while alkanes only exhibit weaker London dispersion forces. Therefore, aldehydes require more energy to overcome their intermolecular forces, resulting in higher boiling points compared to alkanes.