Regelation

When a liquid is heated, the particles gain more energy and move faster, causing the liquid to expand. The most energetic particles at the surface of the liquid escape as vapor, as they gain enough energy to overcome the forces of attraction between them. As the temperature of the liquid increases, more particles acquire the energy needed to break free from the surface. Eventually, even particles in the middle of the liquid form bubbles of gas, and this is when the liquid starts boiling and transforming into gas. The particles in the gas phase are the same as those in the liquid phase but with higher energy.

Evaporation occurs when particles at the surface of a liquid gain enough energy to escape into the air as vapor or gas. Not all particles in a liquid have the same energy; some are more energetic than others. These energetic particles may overcome the attractive forces holding them in the liquid, escaping to become gas. Evaporation can happen at room temperature, which is usually below the boiling point of the liquid. This process occurs only at the surface of the liquid.

Several factors influence evaporation:

Temperature: As the liquid's temperature increases, more particles have enough energy to escape, increasing the rate of evaporation.

Wind: Wind helps remove vapor particles from the liquid, speeding up the process of evaporation.

Evaporation is often seen when puddles of water dry up or when clothes dry in the air.

Latent heat refers to the energy required to change the state of matter without changing its temperature. This heat is called "latent" (hidden) because it does not cause a temperature change, and therefore, it cannot be measured by a thermometer.

1. Specific latent heat is the energy required to change the state of one unit mass of a substance from one state to another, without a change in temperature.
2. Latent heat of fusion is the amount of heat required to convert a solid into a liquid at constant temperature (e.g., melting ice).
3. Latent heat of vaporization is the amount of heat required to convert a liquid into a gas at constant temperature (e.g., boiling water).

Calculate the amount of heat required to melt 800g of ice at 0°C. The specific latent heat of fusion of ice is 33400 J/kg.

Given Data:

Mass of ice,

$M = 800g = 0.8kg$

Specific latent heat of fusion of ice,

$L = 33400 \, \text{J/kg}$

Heat gained,

$H = M \times L$

Substitute the values:

$H = 0.8 \, \text{kg} \times 33400 \, \text{J/kg}$

$H = 26720 \, \text{J}$

Thus, the amount of heat required to melt 800g of ice is 26720 J.

To determine the specific latent heat of fusion of ice, the following steps are followed:

1. Mass of calorimeter + stirrer = $M_1$
2. Mass of calorimeter + water = $M_2$
3. Mass of calorimeter + water after adding ice = $M_3$
4. Initial temperature of water = $Q_1$
5. Final temperature of water = $Q_f$

The mass of water is $M_2 - M_1$, and the mass of ice is $M_3 - M_2$.

The ice melts at 0°C, and the water formed warms up to temperature $Q_f$. The heat gained by the ice during melting at 0°C is given by:

$\text{Heat gained by ice} = (M_3 - M_2) \times L$

The heat gained by the water formed is:

$\text{Heat gained by water} = (M_3 - M_2) \times C_W \times Q_f$

Where:

• $C_W$ is the specific heat capacity of water.

The heat lost by the original water in the calorimeter is:

$\text{Heat lost by original water} = (M_2 - M_1) \times (Q_1 - Q_f) \times C_W$

The heat lost by the calorimeter and stirrer is:

$\text{Heat lost by calorimeter and stirrer} = M_1 \times C_C \times (Q_1 - Q_f)$

Where:

• $C_C$ is the specific heat capacity of the material of the calorimeter.

Now, applying the heat equation:

$\text{Heat gained by ice} + \text{Heat gained by water formed} = \text{Heat lost by calorimeter and stirrer} + \text{Heat lost by original water}$

$(M_3 - M_2) \times L + (M_3 - M_2) \times C_W \times Q_f = M_1 \times C_C \times (Q_1 - Q_f) + (M_2 - M_1) \times C_W \times (Q_1 - Q_f)$

This equation can be used to solve for the specific latent heat of fusion of ice.