Question

What is the melting point of the substance represented by the complete heating curve below? A line graph showing the heating curve of a substance being heated from the solid phase all the way to the gas phase. The substance starts at a temperature around 0°C and ends at a temperature around 70°C. First, there is an incline with a positive slope from 0°C to 20°C, followed by a horizontal region at 20°C. Then there is another incline with a positive slope from 20°C to 60°C, followed by another horizontal region at 60°C. The end of the heating curve shows another incline with a positive slope from 60°C to 70°C.

A. 0°C
B. 20°C
C. 40°C
D. 60°C

Answer 1

Answer: option B. 20°C.

Step-by-step explanation:

1. The melting point is the temperature at which a substance changes from solid to liquid.

2. The phase changes, e.g. melting, boiling, freezing, and condensation, happen at constant temperature.

3. In a temperature vs time diagram, a horizontal (flat) line represents constant temperature.

4. In a temperature vs time diagram, the phases from left to right go from solid to liquid to gas.

4. Hence, the first horizontal region at 20°C is indicating the constant temperature at which the substance is changing from solid to liquid (melting).