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User198
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The specific latent heat, that is divided by the mass, is (by use of your notation):

$$l=\frac{L}{m}$$ where $m$ is the mass of the substance we are examining.

One way to determine the specific latent heat is that it is the difference of enthalpies of the phase transition.

So:

$$l= h''-h'$$

where $h''$ is the enthalpy of the substance when it turned all to vapor (so no more liquid state is present) and $h'$ is when there liquid just starts to boil, so it is all in liquid phase, i.e. before (actually, exactly at the moment) the phase transition starts.

The change of specific internal energy during the phase change can be provided as:

$$\Delta u= h_{2}-h_{1}-p(v_{2}-p_{1})$$

where terms indexed with $1$ represent the states at the beginning of the process and $2$ represents the end of the process. So the process can start even in a "cold" liquid and end in an "overheated" vapor.

So you can see that your equation:

$$\Delta U = L - p\Delta V$$ could be interpreted as correct, but you have to be more precise when writing equations as to exactly specify the start and the end of the process.

The specific latent heat, that is divided by the mass, is (by use of your notation):

$$l=\frac{L}{m}$$ where $m$ is the mass of the substance we are examining.

One way to determine the specific latent heat is that it is the difference of enthalpies of the phase transition.

So:

$$l= h''-h'$$

where $h''$ is the enthalpy of the substance when it turned all to vapor (so no more liquid state is present) and $h'$ is when there liquid just starts to boil, so it is all in liquid phase, i.e. before the phase transition starts.

The change of specific internal energy during the phase change can be provided as:

$$\Delta u= h_{2}-h_{1}-p(v_{2}-p_{1})$$

where terms indexed with $1$ represent the states at the beginning of the process and $2$ represents the end of the process. So the process can start even in a "cold" liquid and end in an "overheated" vapor.

So you can see that your equation:

$$\Delta U = L - p\Delta V$$ could be interpreted as correct, but you have to be more precise when writing equations as to exactly specify the start and the end of the process.

The specific latent heat, that is divided by the mass, is (by use of your notation):

$$l=\frac{L}{m}$$ where $m$ is the mass of the substance we are examining.

One way to determine the specific latent heat is that it is the difference of enthalpies of the phase transition.

So:

$$l= h''-h'$$

where $h''$ is the enthalpy of the substance when it turned all to vapor (so no more liquid state is present) and $h'$ is when there liquid just starts to boil, so it is all in liquid phase, i.e. before (actually, exactly at the moment) the phase transition starts.

The change of specific internal energy during the phase change can be provided as:

$$\Delta u= h_{2}-h_{1}-p(v_{2}-p_{1})$$

where terms indexed with $1$ represent the states at the beginning of the process and $2$ represents the end of the process. So the process can start even in a "cold" liquid and end in an "overheated" vapor.

So you can see that your equation:

$$\Delta U = L - p\Delta V$$ could be interpreted as correct, but you have to be more precise when writing equations as to exactly specify the start and the end of the process.

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User198
User198
  • 904
  • 3
  • 17

The specific latent heat, that is divided by the mass, is (by use of your notation):

$$l=\frac{L}{m}$$ where $m$ is the mass of the substance we are examining.

One way to determine the specific latent heat is that it is the difference of enthalpies of the phase transition.

So:

$$l= h''-h'$$

where $h''$ is the enthalpy of the substance when it turned all to vapor (so no more liquid state is present) and $h'$ is when there liquid just starts to boil, so it is all in liquid phase, i.e. before the phase transition starts.

The change of specific internal energy during the phase change can be provided as:

$$\Delta u= h_{2}-h_{1}-p(v_{2}-p_{1})$$

where terms indexed with $1$ represent the states at the beginning of the process and $2$ represents the end of the process. So the process can start even in a "cold" liquid and end in an "overheated" vapor.

So you can see that your equation:

$$\Delta U = L - p\Delta V$$ could be interpreted as correct, but you have to be more precise when writing equations as to exactly specify the start and the end of the process.