Which ONE of the following compounds has the HIGHEST vapour pressure?
A - NSC Physical Sciences - Question 1 - 2019 - Paper 2
Question 1
Which ONE of the following compounds has the HIGHEST vapour pressure?
A. HCOOH
B. CH3CHO
C. CH3CH2OH
D. CH3CH2CH3
Worked Solution & Example Answer:Which ONE of the following compounds has the HIGHEST vapour pressure?
A - NSC Physical Sciences - Question 1 - 2019 - Paper 2
Step 1
Identify the compounds
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Answer
The provided options are:
A. HCOOH (formic acid)
B. CH3CHO (acetaldehyde)
C. CH3CH2OH (ethanol)
D. CH3CH2CH3 (propane)
Step 2
Analyze their structures and intermolecular forces
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Answer
To determine the vapour pressure, we must consider the intermolecular forces:
HCOOH has hydrogen bonding due to its hydroxyl group.
CH3CHO also exhibits hydrogen bonding.
CH3CH2OH also has hydrogen bonding.
CH3CH2CH3 is a hydrocarbon with weaker Van der Waals forces.
In general, the stronger the intermolecular forces, the lower the vapour pressure.
Step 3
Determine the expected vapour pressures
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Answer
Propane (CH3CH2CH3) is a nonpolar molecule and has the weakest intermolecular forces, leading to the highest vapour pressure compared to the others, which have hydrogen bonding and therefore lower vapour pressures.
Step 4
Final Answer
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Answer
Thus, the compound with the highest vapour pressure is D. CH3CH2CH3.
