{"id":367,"date":"2026-06-30T00:17:04","date_gmt":"2026-06-30T00:17:04","guid":{"rendered":"https:\/\/physicsfundamentalsinfo.com\/blog\/?p=367"},"modified":"2026-06-30T00:21:44","modified_gmt":"2026-06-30T00:21:44","slug":"latent-heat","status":"publish","type":"post","link":"https:\/\/physicsfundamentalsinfo.com\/blog\/thermodynamics\/latent-heat\/","title":{"rendered":"What Is Latent Heat?"},"content":{"rendered":"\n
Definition<\/div>

\n\nLatent heat is the energy a substance absorbs or releases during a change of state \u2014 melting, freezing, boiling or condensing \u2014 without any change in temperature. It is calculated as Q = mL, where the heat energy (Q) equals the mass (m) multiplied by the specific latent heat (L), measured in joules per kilogram, of that particular phase change.\n\n<\/p><\/div>\n

Crank up the hob under a pan of water and the temperature climbs steadily \u2014 until it reaches 100 \u00b0C. Then something odd happens. The flame is still roaring and energy is still pouring in, yet the thermometer simply refuses to move.<\/p>\n

So where is all that energy going? It is being swallowed whole as the water turns to steam, with nothing to show for it on the dial. That hidden energy is latent heat<\/strong>, and it quietly runs everything from a sweaty afternoon to the raw power of a hurricane.<\/p>\n

What Is Latent Heat?<\/h2>\n

Think about ice melting in your hand. It stays stubbornly at 0 \u00b0C the whole time it is turning to water, even though your warm palm keeps feeding it energy. The energy is clearly doing something<\/em> \u2014 but it is not raising the temperature.<\/p>\n

That “something” is the heart of latent heat. Latent heat is the energy absorbed or released when a substance changes state, with no change in its temperature.<\/strong> The word latent<\/em> means hidden \u2014 the energy is hidden inside the rearrangement of the molecules rather than appearing as a hotter reading.<\/p>\n

Every substance has its own latent heat, and it is usually quoted per kilogram. This per-kilogram value is the specific latent heat<\/strong>, given the symbol L<\/strong>. There are two kinds you will meet again and again: the latent heat of fusion (melting and freezing) and the latent heat of vaporisation (boiling and condensing \u2014 US spelling: vaporization<\/em>).<\/p>\n

Contrast this with ordinary heating, where adding energy makes a thermometer rise. That everyday warming is governed by specific heat capacity<\/a>. Latent heat is its quieter cousin: it changes what<\/em> a substance is, not how hot it feels.<\/p>\n

The Latent Heat Formula: Q = mL<\/h2>\n

The amount of energy a phase change needs depends on just two things \u2014 how much stuff you have, and which substance it is. That gives us a refreshingly short equation.<\/p>\n

Q = mL<\/div>\n

Here is what each symbol means, with its SI unit:<\/p>\n