Problem 8 What is latent heat? How is it i... [FREE SOLUTION]

Chapter 7: Problem 8

What is latent heat? How is it involved in the phase changes of water?

Short Answer

Expert verified

Latent heat is the energy absorbed or released by a substance during a phase change. It is responsible for ensuring a constant temperature during the phase changes of water, such as melting, evaporation, and sublimation. For instance, for ice to melt into water or water to evaporate into steam, it must absorb latent heat without any increase in temperature.

Step by step solution

Understand the concept of Latent Heat

Latent heat is the amount of energy absorbed or released by a substance during a constant-temperature process, such as a phase change. The term 'latent' comes from a Latin word Latere, meaning 'to lie hidden.' In the context of phase changes, 'latent' means 'hidden' or 'concealed,' as this heat causes a phase change without changing temperature.

Recognize the role of Latent Heat in phase changes

Latent heat is involved in the phase changes of water. For water to change from a solid (ice) to a liquid (water), or from a liquid to a gas (steam), it must absorb latent heat. The amount of latent heat needed for these transitions is quite substantial and occurs without any rise in temperature. It ensures that the temperature remains constant during phase changes.

Identify the specific phase changes

There are three important phase change processes involved - melt/freeze, evaporate/condense, and sublimate/deposit. The amount of latent heat is reported differently for each phase. It is 'latent heat of fusion' for solid to liquid phase, 'latent heat of vaporization' for liquid to gas phase, and 'latent heat of sublimation' for solid to gas phase.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Phase Changes

Phase changes occur when a substance transitions between different states of matter, such as from solid to liquid, liquid to gas, or even directly from solid to gas. These changes are important because they involve shifts in energy and arrangement of molecules. For a phase change to happen, energy must be absorbed or released, depending on the direction of the change.
When a solid turns into a liquid, it is called melting, while freezing is the opposite process. When a liquid becomes a gas, it is known as vaporization, whereas condensation is when gas turns back into a liquid.

Melting and freezing occur at the melting point, while vaporization and condensation happen at the boiling point.
Phase changes occur without changing the temperature of the substance during the process.
The energy absorbed or released during phase changes is known as latent heat.

Latent Heat of Fusion

The latent heat of fusion describes the heat energy needed to change a substance from solid to liquid or vice versa. This is a crucial concept for understanding how materials like ice melt into water. Latent heat of fusion is the energy required to break the bonds holding the molecules in a solid structure.
When ice melts, it absorbs heat but does not increase in temperature until all ice has turned to water.

Water's latent heat of fusion is particularly significant because it maintains a constant temperature of 0掳C as ice turns into water.
This property allows processes, such as in climate systems, where ice and snow act as thermal buffers, absorbing heat in warmer periods.
Conversely, during freezing, the energy is released without decreasing the temperature of the liquid until it has completely solidified.

Latent Heat of Vaporization

Latent heat of vaporization is the energy required to transform a liquid into a gas. This energy is crucial for processes like boiling water, where the water molecules gain sufficient energy to break free from the liquid's surface as steam.
During this transition, the temperature remains constant at the boiling point鈥�100掳C for water鈥攗ntil all the liquid becomes vapor.

This heat is what provides the energy for steam engines, allowing the conversion of water鈥檚 latent heat into mechanical work.
Additionally, the release of latent heat of vaporization helps in atmospheric phenomena, such as the formation of clouds and storms.
Understanding this concept is key to grasping how cooling systems, like in refrigerators, use latent heat for temperature regulation.

Sublimation

Sublimation is a fascinating phase change where a solid directly turns into a gas without passing through the liquid state. This process is less common but can be observed in substances like dry ice or snow under specific conditions.
Sublimation requires energy input, a form of latent heat called latent heat of sublimation, which enables the solid molecules to break away and become gas molecules.

Sublimation is utilized in freeze-drying technology, preserving food by turning ice directly into vapor.
This process is also observed naturally in the carbon dioxide cycle, where CO2 sublimates from dry ice at atmospheric pressure.
Studying sublimation helps in understanding how certain weathering processes occur, affecting landscapes over time.

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What is latent heat? How is it involved in the phase changes of water?

Short Answer

Step by step solution

Understand the concept of Latent Heat

Recognize the role of Latent Heat in phase changes

Identify the specific phase changes

Key Concepts

Phase Changes

Latent Heat of Fusion

Latent Heat of Vaporization

Sublimation

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