A pure crystalline substance is heated at 1 atm and its temperature is recorded every 30 s
PHYSICS · Multi-part · CBSE · Physics · Thermal Properties of Matter · Thermal Properties of Matter
Problem
A pure crystalline substance is heated at 1 atm and its temperature is recorded every 30 s. The resulting heating curve is described verbally below.
• Segment A: –50 °C to –10 °C — the temperature of the solid rises uniformly.
• Segment B: –10 °C to 0 °C — the temperature remains constant while the sample melts completely.
• Segment C: 0 °C to 75 °C — the temperature of the liquid rises uniformly.
• Segment D: 75 °C to 78 °C — the temperature remains constant while the entire sample vaporizes.
• Segment E: 78 °C to 120 °C — the temperature of the gas rises uniformly.
Using particulate-level reasoning, respond to the following.
(a) Describe the changes in the *average kinetic energy* and the *average potential energy* of the particles during Segment A.
(b) During Segment B the temperature remains constant even though energy is being added. Explain, at the molecular level, how the supplied energy is stored in the system.
(c) Without performing numerical calculations, compare the *magnitude* of the energy absorbed per mole in Segment B with that absorbed in Segment D. Justify your answer by discussing the nature of the intermolecular forces broken during each process and the associated change in particle motion.