Specific Latent Heat of Fusion

Key Stage 4

Specific Latent Heat of Fusion is the energy required to change the state of 1kg of a substance from a solid to a liquid.

The SI Unit of specific latent heat of fusion is the J/kg.

Different materials have a different specific latent heat of fusion.

Specific latent heat of fusion depends on the strength of the bonds holding the particles in fixed positions in the solid.

The specific latent heat of fusion of a material can be found by measuring the energy needed to melt 1kg of the material.


The increase internal energy during the time when the temperature remains constant is the energy required to melt the material. This can be used to calculate the specific latent heat of fusion.

NB: You do not need to remember this equation but you need to be able to use it.

Specific Latent Heat = (Energy Transferred)/(Mass)

\(L_f = \frac{E}{m}\)

Where

\(m\) = The mass of the material.

650J of energy is needed to melt 11g of solder at its melting point. Calculate the specific latent heat of fusion of the solder correct to two significant figures.	An 11kg block of ice at 0°C is heated by an immersion heater until it completely melts. The immersion heater is connected to a Joulemeter which reads 3.7MJ. Calculate the specific latent heat of fusion of the water ice correct to two significant figures.
1. State the known quantities in SI Units E = 650J m = 11g = 11x10^-3kg	1. State the known quantities in SI Units E = 3.7MJ = 3.7x10⁶J m = 11kg
2. Substitute the numbers into the equation and solve. \(L_f = \frac{E}{m}\) \(L_f = \frac{650}{11 \times 10^{-3}}\) \(L_f = 59090 J/kg\) \(L_f \approx 59000 J/kg\)	2. Substitute the numbers into the equation and solve. \(L_f = \frac{E}{m}\) \(L_f = \frac{3.7 \times 10^6}{11}\) \(L_f = 3.36363 \times 10^5 J/kg\) \(L_f \approx 3.4 \times 10^5 J/kg\)