Final answer:
Melting and boiling points on a heating curve are found at the horizontal plateaus, indicating phase changes from solid to liquid and liquid to gas, respectively. These points are influenced by pressure and the unique properties of the substance.
Step-by-step explanation:
To determine the melting and boiling points on a heating curve, look for the plateaus or horizontal lines where temperature remains constant despite the input of heat. These points indicate phase changes where the substance transitions from solid to liquid (melting point) or from liquid to gas (boiling point). For most substances, including water, the melting point occurs at the first plateau where heat is added but the temperature does not change as the solid turns to liquid.
The boiling point is found at the second plateau, where again the temperature remains steady while the liquid turns to gas. Substances like carbon dioxide, however, directly transition from solid to gas (sublimation) at standard pressure and would therefore have only one plateau. The boiling point and melting point are determined by external pressure and the specific properties of the substance.
Heat calculations during these phase changes involve the substance's specific heat as well as latent heats of fusion and vaporization. This knowledge allows for the prediction of a substance's state at any given temperature relative to its phase transition temperatures.