Discussion
A differential scanning calorimetry (DSC) experiment tracks the heat flow into or out of a system as a function of temperature. If the experiments given in the options below are performed at 1 atmospheric pressure, then in which case will the DSC thermogram exhibit a spike, either upward or downward?
Answer: C
The spike appears when heating pure ice from 263 K to 284 K.
A DSC curve shows a peak only where a phase transition absorbs or releases latent heat. Ice melts at 273 K, inside the range 263-284 K, giving an endothermic peak.
The other ranges contain no transition: copper melts at about 1358 K, far above 673 K; water cooled from 323 K to 278 K stays liquid, since it freezes at 273 K; and the Pb-Sn eutectic solidifies at about 456 K (183 °C), above the whole range 323-273 K, so the alloy is already solid.
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