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 of the graph is there... ... only solid present? ... only liquid present? ... only gas present?

Explanation:

• In a heating curve, when only solid is present, the temperature is increasing as heat is added but no phase change (melting) has occurred yet. This is region 1.
• When only liquid is present, the substance has melted (completed the phase change from solid - liquid) and has not yet started boiling (phase change from liquid - gas). This is region 3.
• When only gas is present, the substance has completed boiling (phase change from liquid - gas) and is just increasing in temperature as a gas. This is region 5.

Answer:

• Only solid present: 1
• Only liquid present: 3
• Only gas present: 5