Final answer:
To calculate the energy change on the first plateau of a heating/cooling curve, use the intuitive understanding that energy depends on material mass and phase-specific heat of fusion or vaporization, applying Q = m × ΔH, where Q is heat energy, m is mass, and ΔH is the enthalpy change.
Step-by-step explanation:
To calculate the energy change on the first "plateau" of a heating/cooling curve, which represents a phase change, we don't use a fixed formula, but an intuitive understanding that energy change depends on the mass of the substance and the heat of fusion or vaporization specific to the phase change occurring. This plateau signifies that the substance is undergoing a phase transition, such as melting or boiling, where temperature remains constant as energy is added. Since no temperature change occurs, the specific heat capacity formula is not applied here.
The energy required for the phase transition is calculated using the formula Q = m × ΔH, where Q is the heat energy, m is the mass of the substance, and ΔH represents the enthalpy change of fusion or vaporization. For instance, if water is changing from solid to liquid, the enthalpy of fusion would be used. The precise value of ΔH is a known physical constant for a given substance at a specific pressure.