Physics · Ch 8 — Heat and Thermodynamics
Change of State
Change of State
Matter changes between its three states -- solid, liquid, gas -- through five named processes: melting (solid→liquid), evaporation (liquid→gas), sublimation (solid→gas), freezing/solidification (liquid→solid), and condensation (gas→liquid) (Figure 8.7). During any such change of state, heat is continuously supplied (or removed) while the temperature itself stays perfectly constant, plateauing on a temperature-vs-heat-added graph (Figure 8.8) until the phase change is complete. This "hidden" heat is called latent heat: the latent heat capacity of a substance is the heat needed to change the state of a unit mass, , so (SI unit J kg⁻¹) -- called the latent heat of fusion for solid↔liquid, of vaporization for liquid↔gas, or of sublimation for solid↔gas. The triple point of a substance is the unique tempera …
What this figure shows. A triangular diagram with Solid, Liquid and Gas at its three corners, connected by labelled arrows for every possible transition between them: melting (solid to liquid), solidification (liquid to solid), evaporation (liquid to gas), condensation (gas to liquid), sublimation (solid to gas) and deposition (gas to solid). The diagram is used as a visual map of every named phase-change process a substance can undergo, each of which requires (or releases) latent heat …
What this figure shows. A graph of temperature (y-axis) against energy/heat added (x-axis) for water being heated from solid through to gas. The curve rises steadily as the solid ice warms up, then flattens into a completely horizontal plateau labelled 'Melting' while the solid-to-liquid phase change happens (temperature stays fixed at 0°C even though heat keeps being added), then rises again as the liquid water warms toward its boiling point, then flattens into a second horizontal plateau labelled 'Vaporization' while the liquid boils away into gas (temperature fixed at 100°C), after which the curve resumes rising as the resulting steam is heated further as a gas. The two flat plateaus are the graphical signature of latent heat: heat is being absorbed the …