Question

phase change graph
temperature
time
what is occurring during sections 2 and 4 of the graph above? choose two correct answers.

the substance is increasing in heat
the substance is changing phase
the substance is increasing in temperature
the substance is staying the same phase
the substance is maintaining heat and temperature

Explanation:

• In a phase - change graph, during the flat sections (like sections 2 and 4), the temperature remains constant. This is because the substance is undergoing a phase change (e.g., melting or boiling). Even though the temperature is constant, heat is still being added to the substance (the substance is increasing in heat) to break the intermolecular forces for the phase change.
• The option "the substance is increasing in temperature" is incorrect because the temperature is constant in these sections. The option "the substance is staying the same phase" is incorrect as phase change is occurring. The option "the substance is maintaining heat and temperature" is incorrect because heat is being added (so heat is not maintained constant), only temperature is constant during phase change.

Answer:

• the substance is increasing in heat
• the substance is changing phase