Question

a substance is placed in a closed vessel. the substance is continuously heated and its temperature is monitored, leading to the heating curve below. five regions of the heating curve are labeled with a number

during which numbered region(s) of the graph does the addition of heat lead to a state change? select all that apply.

Explanation:

During a state change (such as melting or boiling), the temperature of a substance remains constant while heat is being added. This is because the heat energy is used to break the intermolecular forces rather than increasing the kinetic energy (and thus temperature) of the particles. Looking at the graph, regions where the temperature is constant (horizontal lines) correspond to state changes.

Answer:

2, 4