To understand how energy changes when we switch between different states, or phases, of matter, we use something called latent heat.

Latent heat is the energy needed to change a substance from one state to another without changing its temperature.

Here are two main phase changes:

1. Melting (From Solid to Liquid): When something melts, like ice turning into water, we use the latent heat of fusion (we call it $L_f$).

   The energy needed to melt the ice can be calculated as: $Q = m \cdot L_f$ Here, $Q$ represents the amount of heat added, and $m$ is the mass of the ice.

2. Vaporization (From Liquid to Gas): When a liquid turns into a gas, like water boiling, we use the latent heat of vaporization (called $L_v$).

   The energy needed to boil the water is: $Q = m \cdot L_v$

Learning about these changes is really important for understanding how energy works in thermodynamics!