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A heating curve plots temperature versus heat added (or time at constant heating rate). For water from solid to gas, five segments appear: (1) ice warming (slope $= 1/mc_{\text{ice}}$), (2) melting plateau at 0 degrees C, (3) water warming (slope $= 1/mc_{\text{water}}$), (4) boiling plateau at 100 degrees C, (5) steam warming.

Key features: flat portions indicate phase changes where latent heat is absorbed at constant temperature. The boiling plateau is much longer than the melting plateau because $L_v = 540$ cal/g far exceeds $L_f = 80$ cal/g. The slope between plateaus depends on the specific heat — steeper for materials with lower specific heat.

During phase changes, internal energy changes (potential energy of molecular bonds) without kinetic energy change (no temperature change). The slope $dT/dQ = 1/(mc)$ provides a direct way to compare specific heats of different phases from the same graph. Ice and steam have similar slopes (similar specific heats), while water's slope is about half (twice the specific heat).