Question

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?

• A. Heating 10 mg of pure Cu from 323 K to 673 K
• B. Cooling pure water from 323 K to 278 K
• C. Heating pure ice from 263 K to 284 K
• D. Cooling a Pb-Sn alloy at the eutectic composition from 323 K to 273 K

Hint:

DSC spikes appear only during phase transitions involving latent heat—look for melting or freezing within the given temperature interval.

Answer 1

The Correct Option is C

In a DSC experiment, a spike appears when a material undergoes a phase change involving latent heat absorption or release. Spikes can be endothermic (upward) or exothermic (downward) depending on the process. Option (A): Copper does not melt within the range 323–673 K (melting point ≈ 1357 K). No phase change → no spike.
Option (B): Water freezes at 273 K, but the cooling ends at 278 K. The freezing point is never crossed → no phase change → no spike.
Option (C): Ice melts at 273 K, and the heating range 263–284 K crosses the melting point. Melting involves latent heat absorption, so DSC shows a clear endothermic spike → spike occurs.
Option (D): A Pb–Sn eutectic alloy undergoes solidification at its eutectic temperature, but this requires precise eutectic composition and cooling below liquidus. However, the question marks only one correct option, and the most definite and guaranteed spike occurs in (C).
Therefore, the only certain phase change in the given temperature ranges is melting of ice in option (C).