Thermodynamics Part 5

Concept:A heating curve shows temperature versus heat added. Temperature stays constant during phase changes (melting and boiling) because the heat is used for latent heat, not raising temperature.Explanation:Start: Ice at $-20^\circ\text{C}$.First slope: Temperature of ice rises to $0^\circ\text{C}$ as heat is added ($Q = mc\Delta T$).First plateau: At $0^\circ\text{C}$, ice melts into water. Temperature stays constant due to latent heat of fusion ($Q = mL_f$).Second slope: Temperature of liquid water rises to $100^\circ\text{C}$.Second plateau: At $100^\circ\text{C}$, water boils into steam. Temperature remains constant due to latent heat of vaporization ($Q = mL_v$).Third slope: Temperature of steam rises to $120^\circ\text{C}$.The correct graph must show this exact pattern: three sloping lines and two horizontal plateaus at $0^\circ\text{C}$ and $100^\circ\text{C}$.Shortcut:Look for a graph that has two horizontal segments: one at $0^\circ\text{C}$ and one at $100^\circ\text{C}$. Only option C matches this requirement.Answer:Option C.