Heat is added to a substance at a constant rate. The substance starts as a solid and is melted; the liquid is heated and vaporized; finally, the vapor is heated. This process is shown in the graph. Which of the following statements is correct?

Question

Quizplus · Accepted Answer

During the solid-to-liquid phase change, the temperature remains constant as heat is added. This is the latent heat of fusion, which is represented by the plateau AB in the graph. During the liquid-to-gas phase change, the temperature also remains constant as heat is added. This is the latent heat of vaporization, which is represented by the plateau CD in the graph. Since the plateau CD is higher up on the graph than the plateau AB, the latent heat of vaporization is greater than the latent heat of fusion. Therefore, choice B is correct. The other choices are incorrect because they are either opposite (choice A) or irrelevant (choices C, D, and E) to the information given in the graph.

Heat Is Added to a Substance at a Constant Rate