Specific latent heat (symbol $l$) is the **amount of heat energy required** to convert unit mass ($1\ kg$) of a substance *from one phase to another*. It is an *intensive property*. The associated formula is:
$$
\begin{equation}\begin{aligned}
Q=ml\\
\end{aligned}\end{equation}
$$
Thus:
$$
\begin{equation}\begin{aligned}
l=\frac{Q}{m}\\
\end{aligned}\end{equation}
$$

#### Example

It requires $4,600,000\ J$ of energy to convert $2\ kg$ of water to that same mass of steam. Find the specific latent heat of vaporization of water.

The

SI Unitfor specific latent heat is thus $Joules\ per\ kilogram\ (Jkg^{-1})$.

### Types of specific latent heats

- Specific latent heat of
*fusion*($l_f$) is the heat energy required to convert unit mass ($1\ kg$) of a substance*from its solid state to its liquid state*. - Specific latent heat of
*vaporization*($l_v$) is the heat energy required to convert unit mass ($1\ kg$) of a substance*from its liquid state to its gaseous state*.

Latent heats are associated with

phase changes.

##### Heating Curve for water

This graph shows us the various temperature changes and phase changes associated with the heating of water.

Credits: Course Hero- When there is a temperature change ($Q=mc\Delta T$), there is no phase change ($Q=ml$) and vice versa
- Sections of the graph which are horizontal (
*gradient is zero*) represent*phase changes* - Sections with
**non-zero gradients**represent**temperature changes**