An unknown pure substance is heated at a constant rate
PHYSICS · Multi-part · CBSE · Physics · Thermal Properties of Matter · Thermal Properties of Matter
Problem
An unknown pure substance is heated at a constant rate, and its temperature is recorded over time. The data reveal two distinct horizontal plateaus: the first at 0 °C lasting 5.0 min, and the second at 80 °C lasting 3.0 min. Between plateaus, the temperature increases linearly with time. No temperature change occurs beyond 120 °C within the duration of the experiment.
(a) Sketch a qualitative heating curve based on the description, clearly labeling the plateaus A and B.
(b) For each plateau, state whether the process occurring is a physical or chemical change, and justify your answer.
(c) The experiment is repeated with twice the mass of the substance but with the same heating rate. Predict qualitatively how the duration of each plateau would change, and explain your reasoning.
(d) If an unexpected color change accompanied plateau B, discuss whether that observation would alter your classification in part (b), providing a rationale.