Question

suppose that figure 1 represents the so - called heating curve for substance a. figure 2 below represents the heating curve for substance b.
what conclusion can be drawn regarding the melting points and boiling points of substance a and substance b?

• substance a has a higher melting point and a higher boiling point than substance b.
• substance b has a higher melting point and a higher boiling point than substance a.
• substance a has the higher melting point but substance b has the higher boiling point.
• substance b has the higher melting point but substance a has the higher boiling point.

Explanation:

Step1: Analyze Melting Points

In a heating curve, the flat segment (constant temperature) during heating represents a phase change. For melting, the temperature at the flat segment (solid - liquid transition) is the melting point. By comparing the temperature of the melting - phase flat segment of Substance A (upper graph) and Substance B (lower graph), we can see that Substance B's melting - phase flat segment is at a higher temperature than Substance A's. So Substance B has a higher melting point.

Step2: Analyze Boiling Points

For boiling (liquid - gas transition), we look at the flat segment at higher temperatures. The temperature of the boiling - phase flat segment of Substance A (upper graph) is higher than that of Substance B (lower graph). So Substance A has a higher boiling point.

Answer:

Substance B has the higher melting point but Substance A has the higher boiling point.