Definition

When the volume variation in phase change ($\Delta V$) changes phase from a liquid to a gas, it can be expressed as:

$\Delta V = V_{\text{gas}} - V_{\text{liquid}}$

Since the volume of the gas is significantly greater than that of the liquid,

$V_{\text{gas}} \gg V_{\text{liquid}}$

we can approximate:

$\Delta V \approx V_{\text{gas}}$

Given that water vapor behaves similarly to an ideal gas, we can state that with the values of the universal gas constant ($R_C$), the number of moles ($n$), the absolute temperature ($T$), and the water vapor pressure unsaturated ($p_v$):



Therefore, the volume variation in phase change ($\Delta V$) is:

$\Delta V = \displaystyle\frac{nRT}{p_v}$

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Image

The measurement of the heat of vaporization is carried out by heating a sample, causing it to evaporate, while simultaneously measuring the heat delivered to the sample. Then, the vapor is cooled and condensed back, and the mass that originally evaporated is measured.

In this way, we can estimate the energy required to evaporate a given mass, which corresponds to ERROR:5238,0 measured in joules per kilogram (J/kg) or joules per mole (J/mol).

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Note

The measurement of heat of vaporization is performed by heating a sample, causing it to evaporate, while simultaneously measuring the heat supplied to the sample. Subsequently, the vapor is cooled and condensed, and the mass that originally evaporated is measured.

This process allows for estimating the energy required to evaporate a given mass, which corresponds to the latent heat measured in J/kg or J/mol.

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Quote

The principle of measuring latent heat involves undergoing a phase change and measuring the required energy, as illustrated in the following image:

In this way, it is possible to estimate the energy required to evaporate a given mass, which corresponds to the latent heat measured in J/kg or J/mol.

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Exercise

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Equation

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