Multiple Choice
Which of the following best describes the process of melting in a phase diagram?
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13. Liquids, Solids & Intermolecular Forces
Phase Diagrams
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A phase change graph for a substance shows a plateau at 45 °C as heat is added at constant pressure. What is the melting point of this substance?
A
100 °C
B
45 °C
C
0 °C
D
25 °C
Verified step by step guidance1
Understand that a phase change graph plots temperature versus heat added at constant pressure, showing plateaus where phase changes occur because the temperature remains constant during the transition.
Identify that the plateau on the graph corresponds to the temperature at which the substance undergoes a phase change, such as melting (solid to liquid) or boiling (liquid to gas).
Recognize that the plateau at 45 °C indicates the temperature at which the substance is changing phase without a temperature increase, meaning this is the melting or boiling point.
Since the problem asks for the melting point and the plateau is at 45 °C, conclude that the melting point of the substance is 45 °C.
Remember that melting point is the temperature at which a solid turns into a liquid at constant pressure, which corresponds exactly to the temperature of the plateau during the solid-liquid phase change.
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