JEE Main · 2024 · 30 Jan 2024 · Shift 2 · Heat & Thermodynamics

Tracking temperature against heat supplied as ice at $-10^{\circ }\text{C}$ converts fully to steam at $100^{\circ }\text{C}$:

1. Temperature rises linearly from $-10^{\circ }\text{C}$ to $0^{\circ }\text{C}$ as heat raises the ice's temperature (specific heat of ice).
2. Temperature stays flat at $0^{\circ }\text{C}$ while ice melts, absorbing the latent heat of fusion.
3. Temperature rises linearly from $0^{\circ }\text{C}$ to $100^{\circ }\text{C}$ as heat raises the water's temperature.
4. Temperature stays flat at $100^{\circ }\text{C}$ while water boils, absorbing the latent heat of vaporization.

Since the latent heat of vaporization ($540\text{cal/g}$) is much larger than the latent heat of fusion ($80\text{cal/g}$), the second flat plateau spans a much larger stretch of heat supplied than the first, on a graph with two rising segments and two plateaus of unequal width.