Answer:
Melting Point = -50 °C
Boiling Point = 50 °C
Step-by-step explanation:
A heating curve displays a substance in its 3 states.
On the graph, each region where the slope is positive represents the substance as a solid, liquid, or gas.
When the slope is 0, this is the temperature point at which the substance's state of matter has changed (i.e., melting or boiling/vaporization point) – also known as a phase transition. Essentially, the 0 slope regions are where the substance is changing from one state of matter to the next.
(When the substance is being heated, it's absorbing energy, but when it reaches a phase transition point, the substance begins to consume energy to change its matter state. That's why the temperature doesn't go up while the substance's internal Energy increases.)
In (Figure 1), where 'x' is Energy (J) and 'y' is Temperature (°C):
Region A (0 J ≤ x ≤ 200 J):
The slope is positive, so the substance is in a constant matter state. Because it's the first sloped region, the substance is in its solid state from -100 °C to -50 °C.
Region B (200 J ≤ x 600 J):
The slope is 0, so the substance has reached a phase transition point. Because the previous region was when the substance was solid, that means that the temperature throughout Region B is the melting point at -50 °C.
Region C (600 J ≤ x ≤ 800 J):
The slope is positive so the substance is in a constant matter state. We've already identified when the substance was solid and when it melted, so now the substance is in its liquid state from -50 °C to 50 °C.
Region D (800 J ≤ x ≤ 900 J):
The slope is 0, and since the previous region was when the substance was a liquid, it's now reached its boiling point at 50 °C.
Region E (900 J ≤ x ≤ 1000 J):
The slope is positive, and we've previously identified all of the transition points and matter states except for one, so the substance is now in its gaseous state after reaching 100°C.
(Once a substance reaches its gaseous state, the Temperature/Energy ratio is constant.)