Solids, Liquids, and Intermolecular Forces: Free-Response Questions for AP Chemistry
Review the following concepts if necessary:
- Structures and Intermolecular Forces for AP Chemistry
- The Liquid State for AP Chemistry
- The Solid State for AP Chemistry
- Phase Diagrams and Phase Changes for AP Chemistry
Answer the following questions. You have 10 minutes. You may not use a calculator. You may use the tables at the back of the book.
The above figure shows a typical phase diagram for a one-component system. Use this diagram to answer the following questions.
- What is point C called? List the characteristics of this point.
- What happens to a substance at point E if the temperature is increased at constant pressure?
- Assume point F is at 0°C and 1 atm. Describe the changes that would occur when moving directly from point F to point G (still at 0°C).
- Solid bismuth is less dense than liquid bismuth. How would this change the appearance of the diagram? Explain.
Answers and Explanations
- Point C is the critical point. Give yourself 1 point if you gave this answer. This is the highest temperature and pressure where the liquid and gas phases can be distinguished. This answer is worth 1 point.
- At point E the substance is a solid. Increasing the temperature, at constant pressure, will cause a horizontal movement to the right. When line AB is reached, the solid will sublime. After line AB is passed, only the vapor is present. You get 1 point for noting a movement to the right. You get 1 point for discussing the change from solid to gas.
- The substance is a solid at point F, and it will remain a solid until line BD is reached. When it reaches line BD, it melts. This is worth 1 point. The substance then passes through the liquid phase until line BC is reached. The substance boils when it reaches line BC. This is worth 1 point.
- The line from B to D would have a negative slope instead of a positive slope. This answer is worth 1 point. The denser phase is more stable at higher pressures. An increase in pressure will cause a change to the denser phase (liquid). The BD line must "lean" to the left so that an increase in pressure will cause a change from solid to liquid. This explanation is worth 1 point.
The maximum score is 8 points.
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