Question

What do phase changes look like on a phase diagram? What happens to the temperature at this point?

a) Vertical lines; temperature increases
b) Horizontal lines; temperature remains constant
c) Diagonal lines; temperature decreases
d) Zigzag lines; temperature fluctuates

Answer 1

Phase changes on a phase diagram are depicted as horizontal lines, indicating that during a phase change, the substance's temperature remains constant despite the addition or removal of heat.

Step-by-step explanation:

Phase changes on a phase diagram are represented by horizontal lines; this corresponds to 'b) Horizontal lines; temperature remains constant.'

When a substance undergoes a phase change, the temperature of the sample does not change. Instead, the phase diagram will show a horizontal line at the temperature where the phase change occurs, indicating that even though heat is being added to or removed from the system, the temperature remains constant as the substance transitions from one phase to another.

For example, the horizontal line at the triple point indicates that all three phases (solid, liquid, and gas) are in equilibrium and can exist simultaneously. The length of the horizontal line can reflect the enthalpy of the phase change, such as the longer horizontal line at the boiling point compared to the melting point, showing a higher enthalpy of vaporization than fusion.