The image below was used in class to teach a very important concept.
The red horizontal lines represent a phase change. To clarify what is seen in the graph, there is no change in temperature (as there’s no slope in the line). Essentially, the equation Q = m L shows the energy being absorbed during those segments of the graph (when the substance is changing state).
“L” represents the specific latent heat of a material (J/kg), “Q” represents the heat energy (J) and “m” represents mass (kg).
The blue diagonal lines represent a change in temperature. To clarify what is seen in the graph, there is a change in temperature (hence the slope). The equation Q = m c ∆T is used to calculate the thermal energy in this segment of the graph.
“Q” represents the heat energy (J), “m” represent the mass (kg), “∆T” represents the change in temperature (K) and “c” represents the specific heat capacity (J/kg * K).