# Releasing Energy from Water: Heat, Latent Heat & Expansion

• John Grover
In summary, there are three sources of energy released when water freezes: the release of heat to lower the temperature to 0°C, the latent heat released during the transition from water to ice, and the expansion energy released as the volume of water increases during the phase change. The expansion energy depends on the surrounding pressure and is equal to pΔV, where p is the pressure and ΔV is the change in volume. This energy is already included in the latent heat and specific heat values. For 1 kg of ice under atmospheric pressure, the expansion energy is approximately 10J.
John Grover
Seems to me there are 3 sources of energy released when water freezes:

Release of heat to lower from whatever temp you start with to 0°C, latent heat released in the transition to from water at 0 to ice at 0, and the expansion energy released as the water increases in volume during the phase change. I sort of no how to calculate the first two bits, but not sure how to quantify the expansion energy.

The expansion energy depends on the pressure in the medium that surrounds the ice.
It's equal to p ΔV, where p is the pressure and ΔV the change in volume.

In a vacuum it would be 0.

for 1 kg of ice under atmospheric pressure, p is about 10^5 N/m^2 and ΔV is 10^-4 m^3,
so the expansion energy is about 10J.

The expansion energy is already included in the latent heat which is usually tabulated as latent heat at constant pressure (and so is the specific heat)

## 1. How is energy released from water?

Energy is released from water through a process called heat transfer. This can happen in three ways: conduction, convection, and radiation. In conduction, heat is transferred through direct contact between molecules. In convection, heat is transferred through the movement of fluids. In radiation, heat is transferred through electromagnetic waves.

## 2. What is latent heat and how does it relate to releasing energy from water?

Latent heat is the energy required to change the state of a substance without changing its temperature. In the case of water, when it changes from a liquid to a gas (such as when it evaporates), it absorbs heat energy. This energy is then released when the water changes back to a liquid state, resulting in the release of energy from water.

## 3. How does the expansion of water play a role in releasing energy?

When water is heated, it expands due to the increased movement of its molecules. This expansion creates pressure, which can be harnessed to do work or produce energy. This is the principle behind hydroelectric power plants, where the force of expanding water is used to turn turbines and generate electricity.

## 4. Is releasing energy from water a sustainable process?

Yes, releasing energy from water can be a sustainable process if it is done in a responsible and efficient manner. Water is a renewable resource, and as long as it is properly managed and conserved, it can continue to provide a source of energy without depleting its supply.

## 5. How is the energy released from water used in everyday life?

The energy released from water is used in a variety of ways in everyday life. It is used to generate electricity, heat homes and buildings, power vehicles, and even in cooking and cleaning. Water is a versatile and essential resource, and its ability to release energy makes it a valuable source for many daily activities.

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