Video Transcript
The graph below shows how the temperature of a solid changes over time when heated. The part of the graph marked X indicates the point at which a change of state from a solid to liquid occurs. At this point, the temperature remains constant despite there being continuous heating. What name is given to the heat required for a change of state to occur? (A) Phase heat, (B) specific heat, (C) excess heat, (D) latent heat, (E) sensible heat.
Solids turn into liquids during the process of melting. The temperature at which this change occurs is called the melting point. A solid does not usually change state to a liquid the moment the temperature reaches its melting point. It ordinarily spends some time at its melting point before its state changes. During this time period, there is continuous heating, but the temperature remains constant. The energy absorbed or released by a substance as its physical state changes at a constant temperature is called latent heat.
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.
In conclusion, the name given to the heat required for a change of state to occur is answer choice (D), latent heat.
