Question

heated to its boiling point temperature. at its boiling point temperature, the addition of heat causes the liquid to transition to a gas at a constant temperature. once all the liquid has boiled, the sample continues to be heated (cautiously), causing the temperature of the gas to increase. this process is depicted in figure 1.

figure 1

there are five labeled points on the line of the graph in figure 1. at which of the labeled points is the sample a mixture of liquid and gas?

• the sample is a mixture of liquid and gas at point c.
• the sample is a mixture of liquid and gas at point d.
• the sample is a mixture of liquid and gas at point e.
• there could never be a mixture of both liquid and gas under these conditions.

Explanation:

Step1: Recall Phase Change Graphs

In a heating curve (temperature vs. time), flat segments represent phase changes (melting, boiling) where two phases coexist. Boiling is liquid to gas transition, so during boiling (flat segment), liquid and gas coexist.

Step2: Analyze Each Point

• Point A: Temperature rising (solid heating, no phase change yet).
• Point B: Flat segment (melting, solid - liquid mixture).
• Point C: Temperature rising (liquid heating, no phase change).
• Point D: Flat segment (boiling, liquid - gas mixture).
• Point E: Temperature rising (gas heating, no phase change).

Answer:

The sample is a mixture of liquid and gas at point D.