LEARNATHON

III

Competition for grade 6 to 10 students! Learn, solve tests and earn prizes!

Learn more### Theory:

Specific latent heat is defined as latent heat expressed per unit mass of a substance. It is denoted by the letter L.

If \(Q\) is the amount of heat energy absorbed or released by the ‘m' mass of a substance during its phase change at a constant temperature, then the specific latent heat is given by

$L=\frac{Q}{m}$

As a result, specific latent heat is the amount of heat energy absorbed or liberated by a unit mass without causing a temperature change during a state change. J/kg is the SI unit for specific latent heat.

Let us look at the example problem.

**1**.

**How much heat energy is required to melt 4 kg of ice? (Specific latent heat of ice = 336 J/g)**

**Given**:

Mass (\(m\)) \(=\) \(4 kg\)

Specific latent heat of ice (\(L\)) \(=\) \(336 J/g\)

**To find**: Heat energy (\(Q\))

$\begin{array}{l}L=\frac{Q}{m}\\ \mathit{By}\phantom{\rule{0.147em}{0ex}}\mathit{rearranging},\phantom{\rule{0.147em}{0ex}}\mathit{the}\phantom{\rule{0.147em}{0ex}}\mathit{formula}\phantom{\rule{0.147em}{0ex}}\mathit{becomes}\\ Q=L\times m\\ Q=336\times 4000\\ Q=1344000\\ \mathit{or}\\ Q=1.3\times {10}^{6}J\end{array}$