What is Heat of Vaporization (enthalpy) - More Science on the Learning Videos Channel скачать в хорошем качестве

What is Heat of Vaporization (enthalpy) - More Science on the Learning Videos Channel

This program begins by defining heat of vaporization is the amount of heat that must be added or given off to vaporize one gram or kilogram of a substance and is expressed as J/g or J/kg. Through real, live footage and animation, students will come to understand what happens during vaporization. Viewers will learn that during a phase change heat is absorbed or given off by a substance but no change in temperature of the substance occurs. The enthalpy of vaporization, (symbol ∆Hvap) also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy (enthalpy) that must be added to a liquid substance, to transform a quantity of that substance into a gas. The enthalpy of vaporization is a function of the pressure at which that transformation takes place. The enthalpy of vaporization is often quoted for the normal boiling temperature of the substance; although tabulated values are usually corrected to 298 K, that correction is often smaller than the uncertainty 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 reduced temperature {\displaystyle T_{r}}T_r{\displaystyle \ll 1}\ll 1. The heat of vaporization diminishes with increasing temperature and it vanishes completely at a certain point called the critical temperature ({\displaystyle T_{r}=1}{\displaystyle T_{r}=1}). Above the critical temperature, the liquid and vapor phases are indistinguishable, and the substance is called a supercritical fluid.