Specific Heat And Latent Heat

Heat added to a substance can do two different things: raise its temperature or change its phase (solid ↔ liquid ↔ gas). These effects are described by specific heat and latent heat.

Specific Heat

Specific heat is the amount of heat required to raise the temperature of unit mass of a substance by 1°C (or 1 K) without changing its phase.
Q = m,c,\Delta T

Where:
(Q) = heat added,
(m) = mass,
(c) = specific heat,
(\Delta T) = temperature change.

Units

• J/kg·K (SI)

Types of Specific Heat

• At constant pressure ((c_p))

• At constant volume ((c_v))

For gases, (c_p > c_v) because extra heat is needed for expansion work.

Examples

• Water has a high specific heat, which is why it is used as a coolant.

• Metals generally have low specific heat and heat up quickly.

Latent Heat

Latent heat is the heat required to change the phase of unit mass of a substance without any change in temperature.
Q = m,L

Where:
(L) = latent heat.

Types of Latent Heat

1. Latent Heat of Fusion – solid to liquid (melting)

2. Latent Heat of Vaporization – liquid to vapor (boiling)

During phase change, temperature remains constant while heat is absorbed or released.

Examples

• Ice melting into water absorbs latent heat of fusion.

• Water converting to steam absorbs large latent heat of vaporization.

Key Differences

Engineering Significance

• Coolants and heat exchangers rely on high specific heat.

• Refrigeration and air conditioning depend on latent heat during evaporation and condensation.

• Steam power plants utilize large latent heat of vaporization for energy transfer.