## Table of Contents

## Latent Heat

Latent heat of a substance is the amount of energy absorbed or released by the substance during a change in its physical state that occurs without changing its temperature.

- SI unit of latent heat is the joule ($\text{J}$).
- The latent heat associated with melting a solid or freezing a liquid is called the latent heat of fusion ($L_{f}$); that associated with vapourizing a liquid or a solid or condensing a vapour is called the latent heat of vaporization ($L_{v}$).

## Specific Latent Heat Of Fusion

Specific latent heat of fusion, l_{f}, of a substance is defined as the amount of heat required to change a unit mass of the substance from solid to liquid state, without any change in the temperature.

$$Q = ml_{f}$$

, where

$Q$ = amount of thermal energy absorbed or released

$m$ = mass of substance

$l_{f}$ = specific latent heat of fusion.

- SI unit of specific latent heat of fusion, $l_f$, is
**joule per kilogram ($\text{J kg}^{-1}$)**

## Specific Latent Heat Of Vapourization

Specific latent heat of vapourization, $l_{v}$, of a substance is defined as the amount of heat required to change unit mass of the substance from liquid state to gas state without a temperature change.

$$Q = ml_{v}$$

, where

$Q$ = amount of thermal energy absorbed or released

$m$ = mass of substace

$l_f$ = specific latent heat of vapourization.

- SI unit of specific latent heat of vapourization, $l_{v}$, of a substance is
**joule per kilogram (****$\text{J kg}^{-1}$**)

## Latent Heat In Terms Of Molecular Behaviour

Latent heat energy is absorbed or given out while a substance undergoes state change. The average kinetic energy of the molecules does not change so that the temperature remains constant.

- During melting, heat absorbed by the solid is used to break the inter-molecular bonds between the molecules of solid substance.
- During vapourization, heat absorbed by the liquid is used to break the inter-molecular bonds completely between the molecules of liquid substance.

## Determining The Specific Latent Heat Of Fusion For Ice

In this section, we will guide you through the steps to determine the specific latent heat of fusion for ice.

**Materials Required:**

- Ice cubes or crushed ice
- Thermometer
- Insulated container
- Heater or heat source
- Stopwatch or timer
- Calorimeter (optional)

**Experimental Procedure:**

**Preparation of Ice:**

Begin by preparing a sufficient amount of ice. You can use ice cubes or crushed ice, but ensure that it is free from impurities that may affect the results.**Insulated Container:**

Place the ice in an insulated container. An insulated container helps to minimize heat exchange with the surroundings, allowing for a more accurate determination of the specific latent heat of fusion.**Initial Temperature Measurement:**

Measure the initial temperature of the ice using a thermometer. This serves as the starting point for the experiment.**Heating the Ice:**

Apply heat to the ice using a heater or a heat source. As the ice absorbs heat, it will start melting and transitioning from a solid to a liquid state.**Continuous Temperature Monitoring:**

Continuously monitor the temperature of the ice as it melts. Record the temperature at regular intervals using the thermometer. It’s essential to maintain a constant temperature during this phase of the experiment.**Time Measurement:**

Simultaneously, use a stopwatch or timer to measure the time taken for the ice to completely melt. This time measurement is crucial for calculating the rate at which heat is absorbed.**Calculation of Specific Latent Heat of Fusion:**

Once the ice has completely melted, calculate the specific latent heat of fusion using the formula:

$$Q = ml_{f}$$

,Where:- $Q$ is the heat energy absorbed (in joules),
- $m$ is the mass of the melted ice (in kilograms),
- $l_f$ is the specific latent heat of fusion for ice (in joules per kilogram). The specific latent heat of fusion can be determined by rearranging the formula:

$l_f = \frac{Q}{m}$ Ensure that all units are consistent to obtain accurate results.

**Calorimeter Option:**

For a more precise determination, you can use a calorimeter to measure the heat absorbed by the melted ice. The calorimeter helps trap the heat and allows for a more controlled environment.

## Determining The Specific Latent Heat Of Vaporization For Water

In this section, we will walk you through the steps to determine the specific latent heat of vaporization for water.

**Materials Required:**

- Water
- Heater or heat source
- Thermometer
- Insulated container
- Stopwatch or timer
- Calorimeter (optional)

**Experimental Procedure:**

**Initial Temperature Measurement:**

Begin by measuring the initial temperature of the water using a thermometer. This provides a baseline for the experiment.**Insulated Container:**

Pour a specific amount of water into an insulated container. Insulation helps minimize heat exchange with the surroundings, ensuring that most of the energy supplied goes into the phase change.**Heating the Water:**

Apply heat to the water using a heater or a heat source. As the water absorbs heat, it will gradually reach its boiling point and transition into vapor.**Continuous Temperature Monitoring:**

Continuously monitor the temperature of the water as it heats up. Record the temperature at regular intervals using the thermometer. It’s essential to maintain a constant temperature during this phase of the experiment.**Boiling Point Observation:**

Observe and record the temperature at which the water starts boiling. The boiling point is a critical reference point for calculating the specific latent heat of vaporization.**Time Measurement:**

Simultaneously, use a stopwatch or timer to measure the time taken for the water to completely vaporize. This time measurement is crucial for calculating the rate at which heat is absorbed.**Calculation of Specific Latent Heat of Vaporization:**

Once the water has completely vaporized, calculate the specific latent heat of vaporization using the formula:

$$Q = ml_v$$

,Where:- $Q$ is the heat energy absorbed (in joules),
- $m$ is the mass of the vaporized water (in kilograms),
- $l_v$ is the specific latent heat of vaporization for water (in joules per kilogram). The specific latent heat of vaporization can be determined by rearranging the formula:

$l_v = \frac{Q}{m}$ Ensure that all units are consistent to obtain accurate results.

**Calorimeter Option:**

For a more precise determination, you can use a calorimeter to measure the heat absorbed during the vaporization process. The calorimeter helps trap the heat and provides a controlled environment.