Specific Heat Capacity And Specific Latent Heat (Copy)

Specific Heat Capacity (c)

Definition:

• The specific heat capacity (c) of a substance is defined as:

  The amount of energy required to raise the temperature of 1 kilogram of the substance by 1 degree Celsius (or 1 kelvin).

Formula:

Q = mcΔT

where:
Q = thermal energy supplied (J)
m = mass of substance (kg)
c = specific heat capacity (J/kg·K)
ΔT = change in temperature (K or °C)

• Note: 1 °C = 1 K change in temperature — hence, the unit is compatible in both cases.

Units of Specific Heat Capacity

• Joules per kilogram per kelvin (J/kg·K)
• This unit indicates the amount of energy required to raise the temperature of 1 kg by 1 K

Practical Meaning

• A substance with a high specific heat capacity requires more energy to heat up and cools down slowly.
• A substance with a low specific heat capacity heats up quickly and loses heat faster.

Written and Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change A2 Level Physics Full Scale Course

Applications of Specific Heat Capacity

• Water as a coolant in engines (high c value absorbs more energy)
• Heating systems and calorimetry
• Climate moderation by large water bodies
• Thermal protection systems (e.g. tiles on spacecraft)

Example Calculation

Q: How much energy is needed to raise the temperature of 2 kg of water from 20 °C to 80 °C?

Given:
m = 2 kg
ΔT = 80 – 20 = 60 °C
c = 4200 J/kg·K

Q = mcΔT = 2 × 4200 × 60 = 504,000 J

Specific Latent Heat (L)

Definition:

• The specific latent heat (L) of a substance is the amount of thermal energy required to change the state of 1 kg of the substance without changing its temperature.
• It is energy required for a phase change, such as:
  • Melting (solid → liquid)
  • Freezing (liquid → solid)
  • Boiling (liquid → gas)
  • Condensation (gas → liquid)

Formula:

Q = mL

where:
Q = energy absorbed or released (J)
m = mass undergoing change (kg)
L = specific latent heat (J/kg)

Units of Specific Latent Heat

• Joules per kilogram (J/kg)

Types of Latent Heat

Written and Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change A2 Level Physics Full Scale Course

Important Points on Latent Heat

• During phase change:
  • Temperature remains constant, even though energy is added or removed.
  • The added energy is used to break or form molecular bonds, not to increase kinetic energy.
• Melting and Boiling:
  • Melting point: temperature where solid turns to liquid
  • Boiling point: temperature where liquid turns to gas
• Graphical Representation:
  • A heating curve shows temperature remaining constant during phase change
  • Horizontal lines in the curve represent latent heat

Example Calculation

Q: How much energy is required to boil 0.5 kg of water at 100 °C?
Given:
L_v (water) = 2.26 × 10⁶ J/kg
m = 0.5 kg

Q = mL = 0.5 × 2.26 × 10⁶ = 1.13 × 10⁶ J

Comparison Table: Specific Heat vs. Specific Latent Heat

Applications of Latent Heat

• Sweating: Body cools as sweat evaporates (latent heat of vaporisation)
• Cooling towers: Use of water evaporation to remove heat
• Refrigeration systems: Use latent heat of vaporisation of refrigerants
• Freezing foods: Freezers remove energy during solidification (latent heat of fusion)

Written and Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions and 11 World Records For Educate A Change A2 Level Physics Full Scale Course

Summary Table