Question

10physicalscience_interim 1_25-26 #13 formula sheet calculator periodic table heat added (kilojoules) which of the following is the best explanation for regions b and d of the curve and why? a the substance freezes or condenses because it is undergoing an exothermic phase change. b the substance melts or boils because it is undergoing an endothermic phase change. c the substance sublimes or deposits because it is undergoing an exothermic phase change. d the substance freezes or boils because it is undergoing an endothermic phase change.

Explanation:

In regions where heat is being added and the temperature remains constant during a phase - change, it is an endothermic process. Melting (solid to liquid) and boiling (liquid to gas) are endothermic phase - changes. Region B likely represents melting and if there was a region D (not shown in full but based on the concept), it could represent boiling. During melting and boiling, heat is absorbed to break the intermolecular forces without changing the temperature.

Answer:

B. The substance melts or boils because it is undergoing an endothermic phase change.