False. A positive slope on a phase change graph indicates that the temperature is constant during a phase change, not increasing.
A positive slope on a phase change graph signifies a constant temperature during a phase transition, not a temperature increase. In this context, heat energy is utilized to alter the substance's state, such as melting or boiling, without changing its temperature.
The graph displays a plateau during the phase change, indicating the maintenance of a consistent temperature until the entire transition is complete. Only after the completion of the phase change does the temperature resume an upward trend.
Therefore, a positive slope does not denote temperature increase but rather a specific phase transition occurring within the substance.