A heating curve illustrates
A) what a substance looks like as it is heated
B) what h appens to the particles of a substance as it is heated. increased
C) what happens to the heat applied as the temperature is
D) the changes in the temperature and physical state of a substance as it is heated.
E) the chemical changes that occur as the substance is heated
The correct answer and explanation is :
The correct answer is: D) the changes in the temperature and physical state of a substance as it is heated.
Explanation (Approx. 300 words):
A heating curve is a graphical representation that shows how the temperature of a substance changes as heat is added over time. It provides crucial information about phase changes (such as melting and boiling) and the behavior of a substance as it transitions between solid, liquid, and gas states.
The x-axis of a heating curve usually represents time or heat added, while the y-axis shows temperature. As heat is applied to a substance, the temperature increases—until the substance reaches a phase change point. At this point, even though heat is still being added, the temperature remains constant. This is because the energy is being used to break intermolecular bonds, not to increase kinetic energy (which would raise temperature).
There are typically five segments in a heating curve for a substance like water:
- Solid heating – Temperature rises as the solid absorbs heat.
- Melting point – Temperature plateaus while the solid melts to liquid.
- Liquid heating – Temperature rises again as the liquid absorbs heat.
- Boiling point – Another plateau as the liquid turns into gas.
- Gas heating – Temperature of the gas rises with added heat.
These plateaus at the melting and boiling points are the phase changes, where physical state changes but not chemical composition. Therefore, a heating curve does not illustrate chemical changes (so choice E is incorrect), nor does it directly describe particle movement (though it is implied), or just show the appearance of the substance (choice A).
In summary, a heating curve shows how a substance’s temperature and physical state change with continuous heating, making option D the most accurate choice.