| English | Specific latent heat |
|---|---|
| Bahasa Melayu | Haba pendam tentu |
| 中文 | 比潜热 |
Definition
The heat needed to change the state of 1 kg of a substance without a change in temperature; measured in J kg⁻¹.
In exam terms
The specific latent heat L of a substance is the heat needed to change the state of 1 kg of that substance without any change in temperature. It is measured in joules per kilogram (J kg⁻¹).
There are two kinds: specific latent heat of fusion (melting) and specific latent heat of vaporisation (boiling).
It is used in Q = mL, where Q is the heat in joules (J), m is the mass in kilograms (kg) and L is the specific latent heat in J kg⁻¹. Worked line: Q = mL = 0.5 kg × 3.34 × 10⁵ J kg⁻¹ = 1.67 × 10⁵ J to melt 0.5 kg of ice at 0 °C. Example of correct use: the specific latent heat of vaporisation of water is about 2.26 × 10⁶ J kg⁻¹.
Do not confuse it with…
Do not confuse specific latent heat with specific heat capacity (c). Specific heat capacity has units J kg⁻¹ °C⁻¹ and applies to a temperature change (Q = mcθ), while specific latent heat has units J kg⁻¹ and applies to a change of state at constant temperature (Q = mL).
In Paper 2 this is usually asked as define specific latent heat of fusion, a calculation using Q = mL, or an experiment to determine its value with an electric heater. Watch the units: leaving in the °C⁻¹ term is a common mistake that shows the two ideas have been mixed up.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)