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Checking Vapor Readings for Two Molecule Shapes 4 questions
Checking Vapor Readings for Two Molecule Shapes
Base your answers on the information provided and your knowledge of chemistry. Use the 2025 Chemistry Reference Tables as needed.
A classroom display compares two model liquids made of nonpolar molecules. The molecules have the same formula and mass. Model P is long and less compact. Model Q is compact. The display predicts stronger attractions when more of the surfaces of two molecules can approach closely.
| Sample | Equilibrium vapor pressure at 30 °C (kPa) | Equilibrium vapor pressure at 40 °C (kPa) |
|---|---|---|
| P | 12 | 20 |
| Q | 22 | 34 |
Question 1
Which property has the same value for both liquids and therefore cannot by itself account for their different vapor pressures?
- Equilibrium vapor pressure at 30 °C
- Equilibrium vapor pressure at 40 °C
- Molecular mass
- Compactness
Question 2
Use the fixed-temperature readings and the contact model to explain why the lower vapor pressure of P is consistent with stronger attractions.
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The class places Q alone in two vessels at 40 °C. The vessels have equal vapor-space volumes but different exposed liquid areas. After one minute the pressure due to vapor is 20 kPa in the smaller-area vessel and 30 kPa in the larger-area vessel. Liquid remains in both.
Question 3
A student says the different one-minute readings prove the two vessels will have different equilibrium vapor pressures. Evaluate the claim using the Q reference data.
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Question 4
Describe how the class could check whether area changes the time to reach equilibrium without changing the final vapor pressure.
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