Enthalpy of vaporization

In <a href="/facts/Thermodynamics/q4hIx3yP">thermodynamics</a>, the enthalpy of vaporization (symbol ∆Hvap), also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy (<a href="/facts/Enthalpy/bBou8lCE">enthalpy</a>) that must be added to a <a href="/facts/Liquid/t9GkLWzt">liquid</a> substance to <a href="/facts/Phase_transition/eLP2BY8R">transform</a> a quantity of that substance into a <a href="/facts/Gas/hVVAoodV">gas</a>. The enthalpy of vaporization is a function of the <a href="/facts/Pressure/eyc37GRG">pressure</a> and temperature at which the transformation (<a href="/facts/Vaporization/0Uxpy1WQ">vaporization</a> or <a href="/facts/Evaporation/tgvIlJys">evaporation</a>) takes place.
The enthalpy of vaporization is often quoted for the <a href="/facts/Normal_boiling_point/E2BK9QoS">normal boiling temperature</a> of the substance. Although tabulated values are usually corrected to 298 <a href="/facts/Kelvin/E3trzC4C">K</a>, that correction is often smaller than the <a href="/facts/Significant_figures/RUfYtpgo">uncertainty</a> in the measured value.
The heat of vaporization is temperature-dependent, though a constant heat of vaporization can be assumed for small temperature ranges and for <a href="/facts/Reduced_temperature/0saS6U1I">reduced temperature</a> Tr ≪ 1. The heat of vaporization diminishes with increasing temperature and it vanishes completely at a certain point called the <a href="/facts/Critical_temperature/pkM7RLJK">critical temperature</a> (Tr = 1). Above the critical temperature, the liquid and <a href="/facts/Vapor/PLlojGug">vapor</a> phases are indistinguishable, and the substance is called a <a href="/facts/Supercritical_fluid/rGkUWb7e">supercritical fluid</a>.

Enthalpy of vaporization open-in-new

Enthalpy of vaporization