Define the term boiling point - NSC Physical Sciences - Question 3 - 2024 - Paper 2
Question 3
Define the term boiling point.
Which ONE of compounds A, B or C is mainly in the liquid phase at 100 °C?
Explain the difference in the boiling points of compounds ... show full transcript
Worked Solution & Example Answer:Define the term boiling point - NSC Physical Sciences - Question 3 - 2024 - Paper 2
Step 1
Define the term boiling point.
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Answer
The boiling point of a substance is the temperature at which its vapor pressure equals the atmospheric pressure. At this temperature, the liquid changes to a gas.
Step 2
Which ONE of compounds A, B or C is mainly in the liquid phase at 100 °C?
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Answer
Compound C, CH₃CH₂CH₂CH₂OH, is mainly in the liquid phase at 100 °C because its boiling point is 118 °C, which is above 100 °C.
Step 3
Explain the difference in the boiling points of compounds A and B.
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Answer
The boiling point of compound A (CH₃CH₂CH₂CHCl₂) is 78 °C, while the boiling point of compound B (CH₃(CH₂)₂CH₂Cl) is 46 °C. The higher boiling point of compound A is due to stronger intermolecular forces; specifically, it has greater dipole-dipole interactions compared to compound B, which has weaker London dispersion forces.
Step 4
Which ONE of these values represents X, the boiling point of compound D?
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Answer
The value that represents X, the boiling point of compound D (CH₃CH₂CH₂CHO), is 75 °C.
Step 5
Fully explain the answer to QUESTION 3.4.1.
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Answer
The boiling point of compound D will be less than that of compound C (118 °C) and more than that of A (78 °C). Since compound D's boiling point is 75 °C, it reflects the weaker intermolecular forces compared to A and the relatively stronger forces compared to B.
Step 6
How will the boiling points of these organic compounds be affected? Choose from INCREASE, DECREASE or REMAIN THE SAME.
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Answer
The boiling point of these organic compounds will DECREASE when the atmospheric pressure is reduced to 83 kPa.
