Use the following to answer question:
-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?
A)The latent heat of fusion is greater than the latent heat of vaporization.
B)The latent heat of vaporization is greater than the latent heat of fusion.
C)The latent heat of vaporization is equal to the latent heat of fusion.
D)The mass of the substance must be known before any statements about the latent heats can be made.
E)The relative sizes of the latent heats depend on the rate at which the heat is added.

Question

Use the following to answer question: 
-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?
A)The latent heat of fusion is greater than the latent heat of vaporization. 
B)The latent heat of vaporization is greater than the latent heat of fusion. 
C)The latent heat of vaporization is equal to the latent heat of fusion. 
D)The mass of the substance must be known before any statements about the latent heats can be made. 
E)The relative sizes of the latent heats depend on the rate at which the heat is added.

Quizplus · Accepted Answer

The portion of the graph that represents the latent heat of fusion is the flat line between points A and B. The portion that represents the latent heat of vaporization is the flat line between points C and D. The slope of the temperature increase is greater for the liquid phase than for the solid or vapor phases. This means that more heat is required to raise the temperature of the liquid phase compared to the solid or vapor phases. Therefore, the latent heat of vaporization must be greater than the latent heat of fusion.

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