What is the definition of latent heat and how does it apply to phase changes?

In summary, latent heat is the amount of energy required to change the state of a substance without changing its temperature. It is usually measured as the amount of heat needed to change the state of a standard reference mass of the substance. For example, the latent heat of vaporization for water is 2257kJ/kg. So, if you vaporize half a kg of water, it would require 1123.5kJ of energy. The rate at which heat is supplied also affects the time it takes to vaporize the water.
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I need some clarifications on the precise definitions and scope of latent heat. My textbook defines latent heat as the amount of energy absorbed or releases during a phase change process. So if I have a pot of liquid water and I vaporize it completely, then the latent heat is simply the energy I had to put into the system to completely vaporize the water? What if I only vaporize half of the liquid water? Would the latent heat be the energy I had to put into the system in order for that to happen or does latent heat not apply to this situation because not all of the water is vaporized?
 
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  • #2
Latent Heat is the amount of energy needed to change the state of a substance without changing it's temperature. That's the concept. The quantity is usually defined to be the amount of heat needed to change the state of a standard reference mass of the substance since it clearly takes more heat to change the state of more substance.

eg. - the latent heat of vaporizaton for water is 2257kJ/kg ... i.e. you need 2257kJ to vaporize 1kg of water at 100degC (at std pressure). If you vaporized half a kg, that would need 1123.5kJ or half as much.

If you supplied 2.257kW of heat to the water, then it would take 1000s to vaporize 1kg of water.
 

Related to What is the definition of latent heat and how does it apply to phase changes?

1. What is latent heat in thermodynamics?

Latent heat in thermodynamics refers to the amount of energy required to change the phase of a substance from solid to liquid or liquid to gas, without changing its temperature. This energy is used to break or form intermolecular bonds between particles.

2. How is latent heat different from specific heat?

Specific heat is the amount of energy required to raise the temperature of a substance by a certain amount. Latent heat, on the other hand, is the energy required to change the phase of a substance at a constant temperature.

3. What are the two types of latent heat?

The two types of latent heat are latent heat of fusion and latent heat of vaporization. Latent heat of fusion is the energy required to change a substance from solid to liquid, while latent heat of vaporization is the energy required to change a substance from liquid to gas.

4. How does latent heat affect the melting and boiling points of a substance?

Latent heat plays a crucial role in determining the melting and boiling points of a substance. When a substance reaches its melting or boiling point, the addition of heat does not result in a temperature change, but instead, the energy is used to break or form intermolecular bonds and change the phase of the substance.

5. What is the significance of latent heat in everyday life?

Latent heat has many practical applications in everyday life. For example, it is the reason why our bodies sweat to cool down, as the evaporation of sweat absorbs energy from the body. It is also used in refrigeration and air conditioning systems, as well as in cooking and food preservation methods such as freezing and drying.

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