13.0     HEAT CAPACITY

Heat capacity is the amount of heat energy required to raise the temperature of a substance by one degree Celsius (or one Kelvin).

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Heat Capacity Formula

C = Q / ΔT

Where                 C is the heat capacity,

Q is the heat added, and

ΔT is the change in temperature.

The SI unit of heat capacity is Joules per Kelvin (J/K).

          13.1     SPECIFIC HEAT CAPACITY

Specific heat capacity is the amount of heat energy required to raise the temperature of one unit mass of a substance by one degree Celsius (or one Kelvin).

Heat Capacity Formula

c = Q / (m * ΔT)

Where                 c is the specific heat capacity,

Q is the heat added,

m is the mass of the substance, and

ΔT is the change in temperature.

The SI unit of specific heat capacity is Joules per kilogram per Kelvin (J/(kg·K)).

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          13.2     METHODS OF DETERMINATION OF HEAT CAPACITY AND SPECIFIC HEAT CAPACITY

• Method of Mixtures: This method involves mixing two substances at different temperatures and measuring the final equilibrium temperature.
• Formula: m₁ * c₁ * (T_Final – T_Initial) = m₂ * c₂ * (T_Final – T_Initial)
• Electrical Method: This method uses an electrical heater to supply a known amount of heat to a substance.

The heat supplied can be calculated using the formula:

Q = I²Rt

Where                          I is the current,

R is the resistance, and

t is the time.

          13.3          LATENT HEAT

Latent heat is the amount of heat energy required to change the state of a substance without changing its temperature.

TYPES OF LATENT HEAT

• Latent Heat of Fusion: The heat required to change a substance from solid to liquid at its melting point.
• Latent Heat of Vaporization: The heat required to change a substance from liquid to gas at its boiling point.

SPECIFIC LATENT HEAT OF FUSION (L_F): The amount of heat required to convert 1 kg of a solid into a liquid without a change in temperature.

Units: Joules per kilogram (J/kg).

SPECIFIC LATENT HEAT OF VAPORIZATION (L_V): The amount of heat required to convert 1 kg of a liquid into a gas without a change in temperature.

Units: Joules per kilogram (J/kg).

          13.4     MELTING

The process of changing from solid to liquid.

CHARACTERISTICS OF MELTING

• Occurs at a specific temperature called the melting point.
• Requires the absorption of latent heat of fusion.

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13.5     EVAPORATION

The process of changing from liquid to gas at any temperature below the boiling point.

CHARACTERISTICS OF EVAPORATION

• Occurs at the surface of the liquid and can happen at any temperature.
• Requires the absorption of latent heat of vaporization.

1.    BOILING

The process of changing from liquid to gas at the boiling point.

CHARACTERISTICS OF BOILING

• Occurs throughout the liquid and involves the entire volume.
• Requires the absorption of latent heat of vaporization.
• Influence of Pressure on Boiling Point: The boiling point of a liquid increases with an increase in pressure. This is why pressure cookers can cook food faster.
• Influence of Pressure on Melting Point: The melting point of a substance can also be affected by pressure. For most substances, an increase in pressure raises the melting point, but for some (like ice), it can lower the melting point.
• Influence of Dissolved Substances on Boiling Point (Elevation): The presence of dissolved substances (like salt in water) raises the boiling point of the solution compared to pure solvent.
• Influence of Dissolved Substances on the Freezing Point (Depression): The presence of dissolved substances lowers the freezing point of the solution compared to pure solvent.

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13.7     APPLICATIONS OF HEAT IN APPLIANCES 

• Refrigerators: Use the principles of latent heat to absorb heat from the interior, causing the refrigerant to evaporate and cool the space.
• Air Conditioners: Utilize the latent heat of vaporization to cool air by evaporating refrigerants.
• Pressure Cookers: Increase the boiling point of water, allowing food to cook faster under higher pressure.