Final answer:
Yes, it is possible for the temperature of a system to remain constant during phase changes, such as melting ice and boiling water.
Step-by-step explanation:
Yes, it is possible for the temperature of a system to remain constant when heat flows into or out of it. This occurs during phase changes, such as melting ice and boiling water.
When heat is added to ice at 0°C, the temperature remains constant until all of the ice has melted into liquid water. Similarly, when heat is added to boiling water at 100°C, the temperature remains constant until all of the liquid water has turned into steam.
During these phase changes, the added heat is used to overcome the attractive forces that hold the more condensed phase together, rather than increasing the system's temperature.