Video Transcript
The following figure shows how the temperature of a substance changes as it melts and then boils. Which number represents the latent heat of melting?
This question gives us a figure with time along the 𝑥-axis and temperature along the 𝑦-axis. The red line in the figure goes up and to the right, meaning that as we move to the right or later in time, the temperature of the substance increases, the red line rises, and the phase changes.
The question asked us to determine which number on the graph represents the latent heat of melting. The latent heat of melting is the energy gained by a substance as it melts at a constant temperature. Put a slightly different way, when changing phases, a substance will gain or lose energy without the temperature changing. The reason the temperature stays the same is because the energy gained or lost changes the distance between the particles and therefore the phase without changing the speed of the particles and therefore the temperature. As a reminder, melting is the transition from a solid state to a liquid state.
So, if we want to identify the latent heat of melting in the figure, we’re looking for the place where there’s a constant temperature during the transition from solid to liquid. Looking at the figure, the constant temperature in between the labels “Solid” and “Liquid” is represented by the number four. It’s worth clarifying that the latent heat of melting is the energy gained during this section of the process and not the temperature at which it happens.
In conclusion, the number that represents the latent heat of melting is number four.
