Question 17 A polyethylene terephthalate (PET) sample is quenched from 280°C to

Question

Question 17 A polyethylene terephthalate (PET) sample is quenched from 280°C to -150°C. The quenched sample is subjected to differential scanning calorimetry heating at 10° C/min. The result is shown in the Figure below. t/°C What happens at the peak labelled A? PET partially crystallizes and at the same time the overall volume of the sample increases PET crystals melt and at the same time the overall volume of the sample increases PET partially crystallizes and at the same time the overall volume of the sample decreases PET crystals melt and at the same time the overall volume of the sample decreases

Explanation / Answer

The increase in specific heat of the PET due to partial crystalisation leads to a decrease in temperature gradient and hence a subsequent fall in the heat flux at A. This is because heat flux is proportional to temperature gradient. Hence the answer is c. Also the volume of sample decreases due to partial crystalisation as crystals have higher density than the parent liquid.

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