The energy to melt or boil a substance without changing its temperature, E = mL, and finding L with a heater.
What you will learn
- Use E = mL for melting and boiling
- Find a specific latent heat from heater readings or a heating curve
- Combine warming and melting in one calculation
Energy to change state
The specific latent heat of a substance is the energy needed to change the state of 1 kg of it with no change in temperature.
energy for a change of state = mass × specific latent heat
E = m L
Energy in J, mass in kg, L in J/kg (given on the equation sheet). Latent heat of fusion: solid to liquid. Latent heat of vaporisation: liquid to gas.
- Melt 0.5 kg of ice at 0 °C; L = 334 000 J/kg
- E = 0.5 × 334 000
- E = 167 000 J
The rest of this lesson and its 9 practice questions are locked.
In this lesson
- Energy to change state
- Measuring L with a heater
- Two steps
- Try it: E = mL
9 practice questions, marked as you go; about 25 minutes in all.
Key terms
Specific latent heat
In this unit: Particle model, density and gas pressure
Density and its required practical, changes of state, specific latent heat, and the particle model of gas pressure, including p₁V₁ = p₂V₂.