Question

in the graph on the video (and the upper right corner), you can see there are 2 flat lines, one between 10 - 20 kj (heat energy) and the other between 40 - 70 kj. 6 heat energy is increasing, but the temperature remains constant. explain what is happening when these \flat lines\ occur. you may wish to watch the simulation again to help answer this question

Explanation:

When heat energy is increasing but temperature remains constant (flat - lines), it is a phase - change process. During phase changes like melting (solid to liquid) or boiling (liquid to gas), the added heat energy is used to break the intermolecular forces rather than increasing the kinetic energy of the molecules, so the temperature doesn't rise.

Answer:

These flat lines represent phase - change processes. During these intervals, the added heat energy is being used to break intermolecular forces instead of increasing the temperature of the substance.