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
Define the term vapour pressure.
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Answer
Vapour pressure is the pressure exerted by a gas in equilibrium with its solid or liquid form in a closed container at a given temperature.
Step 2
Describe the trend in the vapour pressure of the compounds above.
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Answer
The vapour pressure decreases with an increase in molar mass and chain length. 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. Refer to CHAIN LENGTH/MOLAR MASS, STRENGTH OF INTERMOLECULAR FORCES and ENERGY.
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Answer
As the chain length and molar mass increase from 1-propanol to 1-pentanol, the strength of intermolecular forces, such as hydrogen bonding, also increases. Consequently, more energy is needed to overcome these stronger forces in 1-pentanol compared to 1-propanol.
Step 4
Identify the homologous series represented by graphs A and B respectively.
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Answer
Graph A represents aldehydes while Graph B represents alkanes.
Step 5
Explain the difference in the boiling points of the two homologous series represented by graphs A and B. Refer to the TYPE and STRENGTH of the intermolecular forces.
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Answer
Aldehydes exhibit stronger dipole-dipole interactions and London forces compared to alkanes, which mainly contain weaker London forces. As a result, aldehydes have higher boiling points than alkanes, requiring more energy to overcome the intermolecular forces.
