68) This statement asks us to consider the following statements about process 4 and determine which are true.
Choice A: Choice A states that process 4 is the boiling point of the substance. During process 4, the substance is gaining heat, but the temperature is constant, so process 4 is a phase change between either solid and liquid, or liquid and gas. Looking at process 2, I can tell that the substance is gaining heat but not temperature, much like process 4. However, process 2 has a lower temperature than process 4, so process 2 is a phase change between solid and liquid. Thus, process 4 is a phase change between liquid and gas. At boiling point, a substance changes from liquid to gas, so this statement is true.
Choice B: This answer choice states this process depends on the latent heat of vaporization. The equation below is used to calculate the heat energy needed for a phase change.
As we discussed for choice A, process 4 is a phase change from liquid to gas. From the phase change equation above, we can see that the process is dependent on the latent heat. If it were to be a phase change from solid to liquid, the process would be dependent on the latent heat of fusion. However, we know it is dependent on the latent heat of vaporization because it is a phase change from liquid to gas. This means choice B is true as well.
Choice C: This states that the temperature cannot rise until the end of the phase change. We discussed this in choice A. During a phase change, the temperature remains constant, so this is also a true statement.
Choice D: This states that the process is a liquid to gas phase change. This was also discussed in choice A. Process 2 is a solid to liquid phase change, while process 4 is a liquid to gas phase change. Choice D is true as well.
Since choices A, B, C, and D are true, the answer is all of the above, choice E.
Answer: E
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